ExplorIR®-M
Small Footprint Low Power CO2 Sensor
DESCRIPTION
FEATURES
The ExplorIR®-M is a small footprint low power
NDIR CO2 sensor using state-of-the-art solidstate LED optical technology. The low power
LEDs are manufactured in-house, giving GSS
complete control of the CO2 sensor signal chain.
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The ExplorIR®-M is designed for applications
that need to work reliably over a wide range of
conditions and environments and with the
minimum amount of real estate. The sensor is
available in multiple versions, capable of
measuring CO2 levels up to 100%
concentration.
Small footprint, low power CO2 sensor
70ppm typical measurement accuracy
Measurement range up to 100% CO2
Solid state NDIR LED optical technology
UART control and data interface
Built-in auto-zeroing
APPLICATIONS
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Agriculture
Healthcare
Safety
Aerospace
Food packaging
Incubators
Food storage and transportation
BLOCK DIAGRAM
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
TABLE OF CONTENTS
DESCRIPTION........................................................................................................................................... 1
FEATURES ................................................................................................................................................ 1
APPLICATIONS ......................................................................................................................................... 1
BLOCK DIAGRAM ..................................................................................................................................... 1
ORDERING INFORMATION ...................................................................................................................... 4
PACKAGE DRAWING: ExplorIR®-M .......................................................................................................... 5
PIN-OUT DESCRIPTION: ExplorIR®-M ...................................................................................................... 5
ABSOLUTE MAXIMUM RATINGS ............................................................................................................. 6
RECOMMENDED OPERATING CONDITIONS............................................................................................ 6
MECHANICAL SEALING ............................................................................................................................ 6
CO2 PERFORMANCE CHARACTERISTICS .................................................................................................. 7
ELECTRICAL CHARACTERISTICS ............................................................................................................... 8
POWER CONSUMPTION - ExplorIR®-M ................................................................................................... 8
METHOD OF OPERATION ........................................................................................................................ 9
MODE 0 COMMAND MODE .................................................................................................................... 9
MODE 1 STREAMING MODE ................................................................................................................... 9
MODE 2 POLLING MODE ......................................................................................................................... 9
DIGITAL FILTER ...................................................................................................................................... 10
ZERO POINT SETTING ............................................................................................................................ 11
ZERO IN A KNOWN GAS CONCENTRATION ........................................................................................... 11
ZERO IN NITROGEN ............................................................................................................................... 11
ZERO IN FRESH AIR ................................................................................................................................ 11
ZERO POINT ADJUSTMENT.................................................................................................................... 11
AUTO-ZERO FUNCTION ......................................................................................................................... 12
AUTO-ZERO INTERVALS......................................................................................................................... 12
AUTO-ZERO SETTINGS ........................................................................................................................... 12
PRESSURE AND CONCENTRATION LEVEL COMPENSATION .................................................................. 13
ALTITUDE COMPENSATION TABLE ........................................................................................................ 13
CONTROL INTERFACE ............................................................................................................................ 15
CONTROL INTERFACE TIMING - UART MODE ....................................................................................... 15
UART COMMAND PROTOCOL ............................................................................................................... 15
UART OPERATION ................................................................................................................................. 15
UART INTERFACE SUMMARY ................................................................................................................ 16
CO2 LEVEL MEASUREMENT VALUE - Z INFORMATION (0x5A) .............................................................. 18
CO2 LEVEL MEASUREMENT VALUE - z INFORMATION (0x7A) .............................................................. 18
‘.’ COMMAND (0x2E)......................................................................................................................... 18
K COMMAND......................................................................................................................................... 19
K COMMAND (0x4B) ......................................................................................................................... 19
DIGITAL FILTER COMMANDS ................................................................................................................ 19
A COMMAND (0x41) ......................................................................................................................... 19
a COMMAND (0x61).......................................................................................................................... 19
ZERO POINT SETTING COMMANDS ...................................................................................................... 20
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
F COMMAND (0x46) .......................................................................................................................... 20
G COMMAND (0x47) ......................................................................................................................... 21
U COMMAND (0x55) ......................................................................................................................... 21
u COMMAND (0x75) ......................................................................................................................... 21
X COMMAND (0x58) ......................................................................................................................... 21
P COMMAND - CO2 Level for Auto-Zeroing ...................................................................................... 21
P COMMAND – CO2 Level for Zero-Point Setting.............................................................................. 22
AUTO-ZERO INTERVALS......................................................................................................................... 23
@ COMMAND (0x2E) ........................................................................................................................ 23
PRESSURE AND CONCENTRATION COMPENSATION ............................................................................ 24
S COMMAND (0x53) .......................................................................................................................... 24
s COMMAND (0x73) .......................................................................................................................... 24
MEASUREMENT DATA OUTPUTS .......................................................................................................... 24
M COMMAND ................................................................................................................................... 25
Q COMMAND .................................................................................................................................... 25
SERIAL NUMBER AND FIRMWARE VERSION ......................................................................................... 25
Y COMMAND (0x59).......................................................................................................................... 25
CONNECTION DIAGRAM FOR UART INTERFACE ................................................................................... 26
IMPORTANT NOTICE ............................................................................................................................. 27
ADDRESS ............................................................................................................................................... 27
REVISION HISTORY ................................................................................................................................ 28
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
ORDERING INFORMATION
EXPLORIR-M-X-X
X
5
20
60
100
0-5%
0-20%
0-60%
0-100%
X
Temperature Range
E
Extended, -25 to 55°C
Standard 0 to 50°C
Blank
Notes:
Measurement Range
1. Sensors are shipped individually
See separate data sheet for ExplorIR®-M evaluation kit options.
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
PACKAGE DRAWING: ExplorIR®-M
Weight = ~8g
PIN-OUT DESCRIPTION: ExplorIR®-M
PIN
1
2
3
4
NAME
Rx_In
Tx_Out
GND
VDD
TYPE
Digital Input
Digital Output
Supply
Supply
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DESCRIPTION
UART Receive Input
UART Transmit Output
Sensor ground
Sensor supply voltage
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
ABSOLUTE MAXIMUM RATINGS
Absolute Maximum Ratings are stress ratings only. Permanent damage to the ExplorIR® may be
caused by continuously operating at or beyond these limits. The ExplorIR® functional operating
limits and guaranteed performance specifications are given at the test conditions specified.
ESD Sensitive Device. This sensor uses ESD sensitive components. It is
therefore generically susceptible to damage from excessive static voltages.
Proper ESD precautions must be taken during handling and storage of this
device.
CONDITION
Supply Voltages
Voltage Range Digital Inputs
Operating Temperature Range (Ta)
- Standard
- Extended
Storage Temperature Range
Humidity Range (RH), NonCondensing
Operating Ambient Pressure Range
MIN
-0.3V
GND -0.3V
MAX
+6.0V
5V
0°C
-25°C
-40°C
0
+50°C
+55°C
+70°C
95%
500mbar
2bar
RECOMMENDED OPERATING CONDITIONS
PARAMETER
Supply
Ground
SYMBOL
VDD
GND
MIN
3.25
TYP
3.3
0
MAX
5.5
UNIT
V
V
MECHANICAL SEALING
The ExplorIR®-M does not have an air-tight seal between the sensor casing and the main sensor
body.
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
CO2 PERFORMANCE CHARACTERISTICS
Test Conditions Unless Otherwise Specified
VDD = 3.3V, GND = 0V. RH = 0% non-condensing, T= 25°C, Pressure = 1013mbar
PARAMETER
SYMBOL
CO2 measurement
range
TEST
CONDITIONS
MIN
TYP
MAX
UNIT
0
5
0
20
0
60
0
100
%
%
%
%
Accuracy (0-5% sensor)
Accuracy (0-20% sensor)
Accuracy (0-60% sensor)
Accuracy (0-100% sensor)
@25°C, @ 2% CO2
@25°C, @ 12% CO2
@25°C, @ 20% CO2
@25°C, @ 60% CO2
Accuracy
@25°C
±(70, +5%)
0°C to +50°C, after
zero @25°C
±(70, +5%)
ppm
ppm
-25°C to +55°C, after
zero @25°C
±(100, +5%)
ppm
@25°C
±(300, +5%)
0°C to +50°C, after
zero @25°C
-25°C to +55°C, after
zero @25°C
Digital filter setting 16
±(300, +5%)
ppm
ppm
±(1000, +5%)
ppm
6
8.3
ppm
secs
(Peak-Peak) 0-60%
Accuracy
(Peak-Peak) 0-100%
CO2 RMS Noise
Time to Valid
Measurement
After Power-On
Response Time
Digital filter setting
16, dependent on
digital filter setting
±(70, +5%
of reading)
0.8
±(300, +5%
of reading)
ppm
ppm
30
s
Repeatability
From 0ppm to T90
default settings,
limited by diffusion
through membrane
window
@25°C, 0-60%
±70, +5%
@25°C, 0-100%
±300, +5%
Current
Consumption
Peak current when
sampling
Peak at turn-on
ppm
ppm
mA
SLEEP Mode (K2
polling)
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35
40
0.01
mA
mA
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
ELECTRICAL CHARACTERISTICS
PARAMETER
Digital Input/Output
Input HIGH Level
Input LOW Level
Output HIGH Level
Output LOW Level
SYMBOL TEST
CONDITIONS
MIN
TYP
MAX
UNIT
1.0
3.0
0.4
V
V
V
V
V
3.3
I (mA)
0.01
Total
Power
mW
0.03
3.3
1
3.5
1.8
IOH = +1mA
IOL = -1mA
2.6
POWER CONSUMPTION - ExplorIR®-M
Test Conditions Unless Otherwise Specified
VDD = 3.3V, GND = 0V, RH = 0% non-condensing, T= 25°C, Pressure = 1013mbar
SETTING
SYMBOL TEST CONDITIONS
Active, K0 SLEEP
mode, no
measurement
Active, K1 mode
whilst taking
measurements
Default settings
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VDD
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
METHOD OF OPERATION
After power is applied to the ExplorIR®-M, the sensor will automatically start to take CO2
measurements using the Mode 1 default settings, where the sensor is pre-programmed to send CO2
measurement data at 2 readings per second.
The measurement rate is fixed at 2 readings per second at a fixed 9600 baud rate. The sensor will
return the previous CO2 measurement results if the user requests more frequent measurements.
The ExplorIR®-M has 3 potential modes of operation.
MODE 0 COMMAND MODE
In this mode, the sensor is in a SLEEP mode, waiting for commands. No measurements are made.
There is no latency in command responses. All commands that report measurements or alter the
zero-point settings are disabled in Mode 0. Mode 0 is NOT retained after power cycling.
MODE 1 STREAMING MODE
This is the factory default setting. Measurements are reported twice per second. Commands are
processed when received, except during measurement activity, so there may be a time delay of up
to 10ms in responding to commands.
MODE 2 POLLING MODE
In polling mode, the sensor only reports readings when requested. The sensor will continue to take
measurements in the background, but the output stream is suppressed until data is requested. The
sensor will always power up in streaming or polling mode, whichever mode was used before the
power cycle.
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
DIGITAL FILTER
The CO2 gas chamber is illuminated with a nominal 4.25um wavelength LED and the signal received
using a photo-diode. The signal from the photo-diode is processed and filtered by the sensor to
remove noise and provide an accurate CO2 reading. High frequency noise coming from the sampling
process is removed using a proprietary lowpass filter. The digital filter setting can be varied,
allowing the user to reduce measurement noise at the expense of the measurement response time.
The ideal digital filter setting is application specific and is normally a balance between CO2 reading
accuracy and response time. The ExplorIR®-M sensor will also output the raw unfiltered CO2
measurement data. This data can be post processed using alternative filter algorithms.
Filter Effect on Measurement Data Outputs
900
800
CO2 Levels (ppm)
700
600
500
400
Filtered (Z)
300
Unfiltered (z)
200
100
0
1
11
21
41
31
51
# Measurements
The graph above shows the effects of the filter on the CO2 measurement data (Z or z). The unfiltered
output is shown in orange and the filtered output shown in blue.
Filter Response vs. Filter Setting
4500
4000
CO2 Level (ppm)
3500
A=16
3000
A=32
2500
A=64
A=128
2000
T90
1500
1000
500
0
0
50
100
150
200
250
300
350
400
# Measurements
The graph above shows the effect of the filter on response times. Increasing the filter setting
increases the measurement output response time. T90 is the time to 90% of reading. The ExplorIR®M takes 2 readings per second.
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
ZERO POINT SETTING
There are a several methods available to the user to set the zero point of the sensor. The
recommended user method is zero-point setting in a known gas concentration. In all cases, the best
zero is obtained when the gas concentration is stable, and the sensor is at a stabilised temperature.
Note that zero-point settings are not cumulative and only the latest zero-point setting is effective.
For example, there is no benefit in zeroing in nitrogen, and then zeroing in a calibration gas. The
sensor will store only the latest zero point.
To improve zeroing accuracy, the recommended digital filter setting is 32. See the ‘A’ command.
ZERO IN A KNOWN GAS CONCENTRATION
Place the sensor in a known gas concentration, power up the sensor and allow time for the sensor
temperature to stabilise, and for the gas to be fully diffused into the sensor.
Send the ZERO IN A KNOWN GAS CONCENTRATION command X to the sensor. The sensor will be
zeroed using the known gas concentration level sent by the user. The concentration value written to
the sensor must be scaled dependent on the sensor CO2 measurement range. The multiplier for the
scaling factor is set according to the range of the sensor, see the ‘.’ command.
ZERO IN NITROGEN
Place the sensor in nitrogen gas and allow time for the sensor temperature to stabilise and the gas
to be fully diffused into the sensor. Send the ZERO IN NITROGEN command U to the sensor. The
sensor is zeroed assuming a 0ppm CO2 environment.
ZERO IN FRESH AIR
If there is no calibration gas or nitrogen available, the sensor zero point can be set in fresh air.
Ambient CO2 concentrations in fresh air are typically 400ppm. The CO2 concentration fresh air zero
level is programmable over a range from 0ppm to the full scale of the sensor.
Place the sensor in a fresh air environment and allow time for the sensor temperature to stabilise,
and for the fresh air to be fully diffused into the sensor. Power up the sensor, write the G command
to the sensor. The concentration value written to the sensor must be scaled dependent on the
sensor CO2 measurement range. The sensor can use the default fresh air CO2 concentration value
(400ppm), or the user can write a different fresh air value to the sensor if desired.
ZERO POINT ADJUSTMENT
If the CO2 concentration and the sensor reported concentration are known, the zero point can be
adjusted using the known concentration to fine tune the zero point. For example, if the sensor has
been in an environment that has been exposed to outside air, and the sensor reading is known at
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
that time, the zero point can be fine-tuned to correct the reading. This is typically used to
implement automated zeroing routines.
The known CO2 concentration value and the reported CO2 value from the sensor can be sent to the
sensor using the ZERO POINT ADJUSTMENT command F.
AUTO-ZERO FUNCTION
The sensor has a built-in auto-zero function. To function correctly, the sensor must be exposed to
typical background levels (400-450ppm) at least once during the auto-zero period. For example,
many buildings will drop quickly to background CO2 levels when unoccupied overnight or at
weekends. The auto-zero function uses the information gathered during these periods to recalibrate. The sensor will reset the ‘zero’ level every time it does an auto-zero. Auto-zeroing is
disabled by default. If the sensor is powered down, the auto-zeroing is reset to default values.
The auto-zero function works in the same way as the ZERO IN FRESH AIR command. Auto-zero is
disabled by default, but can be enabled to operate automatically, or zeroing can be forced. The user
can also independently adjust the CO2 level used for auto-zeroing. Typically, it is set to the same
value as the ZERO IN FRESH AIR value, but it can also be set at a different level if desired.
AUTO-ZERO INTERVALS
The auto-zero period can be programmed by the user. The sensor can be programmed to undertake
an initial auto-zero after power-on. Thereafter, the auto-zero period can be set independently of
the start-up zero setting time. Note, the auto-zero settings are reset if the sensor is powered down.
AUTO-ZERO SETTINGS
By default, the sensor will automatically ‘zero’ using the measured CO2 level sampled during the
auto-zero period. The user can alter the behaviour of the sensor because of the auto-zeroing
process.
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
PRESSURE AND CONCENTRATION LEVEL COMPENSATION
NDIR gas sensors detect the concentration of gas by measuring the degree of light absorption by the
gas analyte. The degree of light absorption is converted into a concentration reported by the sensor.
The absorption process is pressure and gas concentration dependent. In general, as the pressure
increases, the reported gas concentration also increases. As the pressure decreases, the reported
concentration decreases. This effect takes place at a molecular level and is common to all NDIR gas
sensors.
GSS sensors readings will vary due to pressure and CO2 concentration. It is possible to correct for
the effects of pressure and concentration by setting a compensation value. This will apply a
permanent correction to the output of the sensor, depending on the compensation value. The
compensation value needs to be written to the sensor and will overwrite the default value. The new
compensation value will be used for all subsequent measurements and will be retained after a
power cycle.
ALTITUDE COMPENSATION TABLE
Altitude
(ft.)
Altitude
(m)
Pressure
(mbar)
Sea Level
Difference
%
Change
per
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
6,000
7,000
8,000
9,000
10,000
0
153
305
458
610
763
915
1,068
1,220
1,373
1,525
1,830
2,135
2,440
2,745
3,050
1,013
995
977
960
942
925
908
891
875
859
843
812
782
753
724
697
0
18
36
53
71
88
105
122
138
154
170
201
231
260
289
316
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.14
CO2
Measurement
Change (%)
0
3
5
7
10
12
15
17
19
22
24
28
32
36
40
44
Compensation
Value
8,192
8,398
8,605
8,800
9,006
9,201
9,396
9,591
9,775
9,958
10,142
10,497
10,841
11,174
11,506
11,816
Other compensation values can be calculated using the following formula.
𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽 = 𝟖𝟖𝟖𝟖𝟖𝟖𝟖𝟖 + �
𝑺𝑺𝑺𝑺𝑺𝑺 𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳 𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫 ∗ 𝟎𝟎. 𝟏𝟏𝟏𝟏
� ∗ 𝟖𝟖𝟖𝟖𝟖𝟖𝟖𝟖
𝟏𝟏𝟏𝟏𝟏𝟏
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
The pressure compensation values calculated above are only approximate and only valid for
concentrations below 1%. For higher accuracy compensation, the sensor output must be adjusted
for both pressure and concentration as the CO2 level measured by the sensor is affected by both
ambient pressure and gas concentration levels. To calculate the adjusted CO2 level, use the
following calculator.
The corrected CO2 level (C2) = C1/(1+Y(1013-P)),
where,
C1 = Concentration reading from sensor
P = Pressure in mbar
Where concentration < 1500ppm.
Y = 2.6661E-16 C14 - 1.1146E-12 C13 + 1.7397E-09 C12 - 1.2556E-06 C1 - 9.8754E-04
Where concentration >1500ppm.
Y = 2.37472E-30 C16 - 2.70695E-25 C15 + 1.24012E-20 C14 - 2.91716E-16 C13 + 3.62939E-12 C12 1.82753E-08 C1 - 1.35129E-03
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
CONTROL INTERFACE
The ExplorIR® family of sensors are controlled by writing and reading from the sensor via its UART
interface. The Rx_In and Tx_Out pins are normally high, suitable for direct connection to a UART. If
the sensor is to be read by a true RS232 device (e.g. a PC), it is necessary to pass through a level
converter to step up/down the voltage and invert the signal.
CONTROL INTERFACE TIMING - UART MODE
PARAMETER
Baud Rate
Data Bits
Parity
Stop Bits
Hardware Flow Control
SYMBOL
MIN
TYP
9600
8
None
1
None
MAX
UNIT
Bits/s
UART COMMAND PROTOCOL
All UART commands must be terminated with a carriage return and line feed , hex 0x0D
0x0A. In this document, this is shown as ‘\r\n’. UART commands that take a parameter always have
a space between the letter and the parameter. The sensor will respond with a ‘?’ if a command is
not recognised. The two most common causes are missing spaces or missing terminators.
All command communications are in ASCII and are terminated by carriage return, line feed (0x0D
0x0A). This document uses the protocol “\r\n” to indicate the carriage return line feed. All
responses from the sensor, including measurements, have a leading space (ASCII character 32).
The character ‘#’ represents an ASCII representation of a numeric character (0-9). Note there is a
space between the first letter and any parameter. For example, the X command reads “X space 2000
carriage return line feed”.
UART OPERATION
When initially powered, the sensor will immediately start to transmit a CO2 reading on receiving any
character.
The CO2 measurement is reported as:
Z #####\r\n
where Z ##### shows the CO2 concentration.
Note that all outputs from the sensor have a leading space.
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
UART INTERFACE SUMMARY
Syntax
Use
Example
Response
A ###\r\n
Set value of the
digital filter
Return the value of
the digital filter
Fine Tune the zero
point
Zero-point setting
using fresh air
Switches the sensor
between different
modes
Sets the number of
measurement data
types output by the
sensor
Sets value of CO2
background
concentration in ppm
for auto-zero
A 128\r\n
A 00128\r\n
See “Digital Filter”
a\r\n
a 00128\r\n
See “Digital Filter”
F 410 400\r\n
F 33000\r\n
G\r\n
G 33000\r\n
See “Zero Point
Setting”
See “Zero Point
Setting”
K 1\r\n
K 1\r\n
M 212\r\n
M 212\r\n
Sets value of CO2
background
concentration in ppm
used for zero- point
setting in fresh air.
P 10 1\r\n
P 11 144\r\n
Reports the latest
measurement data
types, as defined by
‘M’
Sets the pressure and
concentration
compensation value
Returns the pressure
and concentration
compensation value
Zero-point setting
using nitrogen
Manual setting of the
zero point.
Zero-point setting
using a known gas
calibration
Return firmware
version and sensor
serial number
Return the most
recent filtered CO2
measurement in ppm
Q\r\n
H 12345 T 12345 Z
00010\r\n
S 8192\r\n
S 08192\r\n
s\r\n
s 08192\r\n
U\r\n
U 33000\r\n
u 32997\r\n
u 32997\r\n
X 2000\r\n
X 32997\r\n
Y\r\n
Returns two lines
Z\r\n
Z 01521\r\n
a\r\n
F ##### #####\r\n
G\r\n
K #\r\n
M ###\r\n
P 8 ###\r\n
P 9 #\r\n
P 10 ###\r\n
P 11 #\r\n
Q\r\n
S #####\r\n
s\r\n
U\r\n
u #####\r\n
X #####\r\n
Y\r\n
Z\r\n
See “Output Fields”
P 8 1\r\n
P 9 144\r\n
Two-byte value,
P 8 = MSB
P 9 = LSB
400ppm in the
example
Two-byte value,
P 8 = MSB
P 9 = LSB
400ppm in the
example
Gas Sensing Solutions Ltd.
Page | 16
Comments
For regular updates, go to https://www.gassening.co.uk
See “Pressure and
Concentration
Compensation”
See “Pressure and
Concentration
Compensation”
See “Zero Point
Setting”
See “Zero Point
Setting”
See “Zero Point
Setting”
Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
Syntax
Use
z\r\n
@ #.# #.#\r\n
@ r\n
@ #r\n
.\r\n
Return the most
recent unfiltered CO2
measurement in ppm
Sets the timing for
initial and interval
auto-zero periods
Returns the Autozero configuration
Switch Auto-zeroing
on or off
Returns the scaling
factor multiplier
required to convert
the Z or z output to
ppm
Example
Response
Comments
@ 1.0 8.0\r\n
@ 1.0 8.0\r\n
See “Auto-zeroing” for
details
@ 1.0 8.0\r\n
@ 1.0 8.0\r\n
@ 0\r\n
@ 0\r\n
.\r\n
. 00010\r\n
See “Auto-zeroing” for
details
See “Auto-zeroing” for
details
Multiply by 10 in the
example
z\r\n
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Z 01521\r\n
Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
CO2 LEVEL MEASUREMENT VALUE - Z INFORMATION (0x5A)
Description
Syntax
Example
Response
Reports the latest filtered CO2 measurement
ASCII Character 'Z', terminated by 0x0D 0x0A (CR & LF)
Z\r\n
Z 00521\r\n
This value needs to be multiplied by the appropriate scaling factor to derive the ppm value. See the
‘.’ command.
CO2 LEVEL MEASUREMENT VALUE - z INFORMATION (0x7A)
The sensor is also capable of reporting the real time unfiltered CO2 measurement value.
Description
Syntax
Example
Response
Reports the unfiltered CO2 measurement
ASCII Character 'Z', terminated by 0x0D 0x0A (CR & LF)
z\r\n
z 00521\r\n
‘.’ COMMAND (0x2E)
To calculate the measurement value in ppm, the ‘Z’ or ‘z’ value, they must be converted into ppm by
using the ‘.’ multiplier factor. This multiplier will depend on the full-scale measurement range of the
sensor. The multiplier is related to the full-scale range of the sensor.
The multiplier must also be used when sending CO2 concentration levels to the sensor, for example
when setting the fresh air CO2 concentration value. The ‘.’ Command can also be used to read back
the scaling factor.
For example, if the user wants to zero the sensor in a known concentration of gas (e.g. 450ppm), the
value written to the sensor must be 450/scaling factor.
Description
Syntax
Example
Response
Returns a number indicating what multiplier must be applied to the Z CO2
measurement output to convert it into ppm.
ASCII character '.', terminated by 0x0D 0x0A ( CR & LF )
.\r\n
. 00010\r\n
(this number is variable, usually 10)
Measurement
Range of Sensor
CO2 Measurement
Scaling Factor (Z)
CO2 Measurement
Output Units
Example
0 – 60%
10
ppm/10
Z 01200 = 12,000ppm = 1.2%
0 – 100%
100
ppm/100
Z 01500 = 150,000ppm = 15%
Gas Sensing Solutions Ltd.
Page | 18
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
K COMMAND
Command
Use
Default
K #\r\n
Switches the
sensor between
different control
modes
1
Range
Example
Response
Comments
K 1\r\n
K 1\r\n
See ‘K’ Commands
K COMMAND (0x4B)
Description
Syntax
Sets the control interface mode
ASCII character 'K', SPACE, mode number, terminated by 0x0D 0x0A (CR &
LF)
K 1\r\n
K 00001\r\n
(this number is variable)
Example
Response
DIGITAL FILTER COMMANDS
Command
Use
Default
Range
Example
Response
A ###\r\n
Set value of the
digital filter
16
065635
A 16\r\n
A 00016\r\n
a\r\n
Return value of
digital filter
065365
a\r\n
a 00016\r\n
Comments
A COMMAND (0x41)
Description
Syntax
Example
Response
Set the value for the digital filter
ASCII character 'A', SPACE, decimal, terminated by 0x0D 0x0A (CR & LF)
A 16\r\n
A 00016\r\n
(this number is variable)
a COMMAND (0x61)
Description
Syntax
Example
Response
Set the value for the digital filter
ASCII character 'A', SPACE, decimal, terminated by 0x0D 0x0A (CR & LF)
A 16\r\n
A 00016\r\n
(this number is variable)
Gas Sensing Solutions Ltd.
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
ZERO POINT SETTING COMMANDS
Command
Use
Range
Example
Response
Comments
F #####
#####\r\n
Fine Tune the
zero point
Range of
sensor
F 410
400\r\n
F 33000\r\n
See “Zero Point
Setting”
G\r\n
Zero-point
setting using
fresh air
G\r\n
G 33000\r\n
See “Zero Point
Setting”
U\r\n
Zero-point
setting using
nitrogen
U\r\n
U 33000\r\n
See “Zero Point
Setting”
u #####\r\n
Manual setting
of the zero
point
u
32997\r\n
u 32997\r\n
See “Zero Point
Setting”
X #####\r\n
Zero-point
setting using a
known gas
concentration
X 2000\r\n
X 32997\r\n
See “Zero Point
Setting”
P 8 ###\r\n
P 9 #\r\n
Sets value of
CO2
background
concentration
in ppm for
auto-zeroing
P 8 1\r\n
P 9 144\r\n
Sets value of
CO2
background
concentration
in ppm used
for zero- point
zeroing in
fresh air.
P 10 1\r\n
P 11 144\r\n
P 10 ###\r\n
P 11 #\r\n
Default
Range of
sensor
Two-byte value,
P 8 = MSB
P 9 = LSB
400ppm in the
example
Two-byte value,
P 8 = MSB
P 9 = LSB
400ppm in the
example
F COMMAND (0x46)
Description
Syntax
Example
Response
Sets the zero-point using a known reading and a known CO2 concentration
terminated by 0x0D 0x0A (CR & LF)
ASCII character 'F', SPACE, then the reported gas concentration, SPACE, then
the actual gas concentration, terminated by 0x0D 0x0A (CR & LF)
F 41 39\r\n
F 33000\r\n
(the numbers are variable)
Gas Sensing Solutions Ltd.
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
G COMMAND (0x47)
Description
Syntax
Example
Response
Sets the zero point assuming the sensor is in fresh air (typically 400ppm CO2,
but level can be set by user – see P commands.)
ASCII character 'G' terminated by 0x0D 0x0A (CR & LF)
G\r\n
G 33000\r\n
(the number is variable)
U COMMAND (0x55)
Description
Syntax
Example
Response
Sets the zero point assuming the sensor is in 0ppm CO2 such as nitrogen.
ASCII Character 'U' terminated by 0x0D 0x0A (CR & LF)
U\r\n
U 32767\r\n(the number is variable)
u COMMAND (0x75)
Description
Syntax
Example
Response
Forces a specific zero set point value.
Input value is scaled by CO2 value multiplier, see ‘.’ command.
ASCII character 'u', SPACE, then the gas concentration, terminated by 0x0D
0x0A (CR & LF)
u 32767\r\n
u 32767\r\n
X COMMAND (0x58)
Description
Syntax
Example
Response
Sets the zero point with the sensor in a known concentration of CO2. Input
value is scaled by CO2 value multiplier, see ‘.’ command.
ASCII character 'X', SPACE, then the gas concentration, terminated by 0x0D
(CR & LF)
X 1000\r\n
X 33000\r\n
(the number is variable).
P COMMAND - CO2 Level for Auto-Zeroing
Description
Syntax
Example
Response
Sets the value of CO2 in ppm used for auto-zeroing.
Input value is scaled by CO2 value multiplier, see ‘.’ command.
ASCII character 'P', SPACE, then 8, SPACE, then MSB terminated by 0x0D
0x0A (CR & LF)
ASCII character 'P' then a space, then 9, then a space, then LSB terminated
by 0x0D 0x0A (CR & LF)
P 8 0\r\n
P 9 40\r\n
p 8 0\r\n
p 9 40\r\n
Gas Sensing Solutions Ltd.
Page | 21
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
The value is entered as a two-byte word, MSB first.
MSB = Integer (Concentration/256)
LSB = Concentration – (256*MSB)
In the above example, target CO2 background concentration is 400ppm.
MSB = Integer (400/256) = 1
LSB = 400 – 256 = 144
P COMMAND – CO2 Level for Zero-Point Setting
Description
Syntax
Example
Response
Sets value of CO2 in ppm for zero-point setting in fresh air.
Input value is scaled by CO2 value multiplier, see ‘.’ command.
ASCII character 'P', SPACE, then 10, SPACE, then MSB terminated by 0x0D
0x0A (CR & LF)
ASCII character 'P', SPACE, then 11, SPACE, then LSB terminated by 0x0D
0x0A (CR & LF)
P 10 7\r\n
P 11 208\r\n
p 10 7\r\n
p 11 208\r\n
MSB = Integer (Concentration/256)
LSB = Concentration – (256*MSB)
In the above example, target zero-point CO2 concentration is 2000ppm.
MSB = Integer (2000/256) = 7
LSB = 2000 – (256*MSB) = 208
Gas Sensing Solutions Ltd.
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
AUTO-ZERO INTERVALS
UART
Command
Use
Default
@ #.# #.#\r\n
Auto-zero
interval
settings
Range
Example
Response
Comments
@ 1.0 8.0\r\n
@ 1.0 8.0\r\n
See “Auto-zeroing
function” for
details
@ COMMAND (0x2E)
Description
Syntax
Example
Response
Set the ‘Initial Interval’ and ‘Regular Interval’ for auto-zeroing events.
ASCII character '@', SPACE, decimal, SPACE, decimal terminated by 0x0D
0x0A (CR & LF)
@ 1.0 8.0\r\n
@ 1.0 8.0\r\n (the number mirrors the input value)
Both the initial interval and regular interval are given in days. Both must be entered with a decimal
point and one figure after the decimal point. In the above example, the auto-zero interval is set to 8
days, and the initial interval set to 1 day.
To disable auto-zeroing, send @ 0\r\n.
To start an auto-zero immediately, send 65222\r\n.
To determine the auto-zero configuration, send @\r\n.
Gas Sensing Solutions Ltd.
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
PRESSURE AND CONCENTRATION COMPENSATION
UART
Command
Use
Default Range
Example
Response
Comments
S #####\r\n
Sets the pressure
and concentration
compensation value
8192
S 8192\r\n
S 08192\r\n
See “Pressure and
Concentration
Compensation”
s\r\n
Returns the
pressure and
concentration
compensation value
s\r\n
s 08192\r\n
See “Pressure and
Concentration
Compensation”
0-65536
S COMMAND (0x53)
Description
Syntax
Example
Response
Set the ‘Pressure and Concentration Compensation' value
ASCII character 'S', SPACE, decimal, terminated by 0x0D 0x0A (CR & LF)
S 8192\r\n
S 8192\r\n
(the number mirrors the input value)
s COMMAND (0x73)
Description
Syntax
Example
Response
Reports the ‘Pressure and Concentration Compensation' value.
ASCII Character 's', terminated by 0x0D 0x0A (CR & LF)
s\r\n
s 8192\r\n
MEASUREMENT DATA OUTPUTS
The ExplorIR®-M sensor can provide filtered and unfiltered CO2 data as a single string of data.
UART
Command
Use
Default
M #####\r\n
Sets the number of
measurement data
types output by
the sensor. #####
is the mask value
M 00006\r\n
Measurement Parameter
CO2 (Filtered)
CO2 (Unfiltered)
Range
Field Identifier
Z
z
Example
Response
Comments
See “Output
Fields”
M #####\r\n
Sets the number of
measurement data
types output by
the sensor
Mask Value
4
2
The required mask value is the sum of the ‘Mask Value’ for each field required. To output filtered
and unfiltered CO2 data, set M=6.
Gas Sensing Solutions Ltd.
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
M COMMAND
Description
Syntax
Example
Response
Sets the type and number of data outputs
ASCII character 'M', terminated by 0x0D 0x0A ( CR & LF )
M\r\n
M 04164\r\n
Q COMMAND
Description
Syntax
Reports the number of output data fields
ASCII character 'Q', SPACE, then Mask Value, terminated by 0x0D 0x0A ( CR
& LF )
Q\r\n
Z 00010\r\n
Example
Response
SERIAL NUMBER AND FIRMWARE VERSION
UART
Command
Use
Default Range
Y\r\n
Return
firmware
version and
sensor serial
number
Example
Response
Y\r\n
Returns two
lines
Comments
Y COMMAND (0x59)
Description
Syntax
Example
Response
The present version string for the firmware and serial number of the sensor.
ASCII character 'Y', terminated by 0x0D 0x0A ( CR & LF )
Y\r\n
Y,Jan 30 2013,10:45:03,AL17\r\n
ingB 00233 00000\r\n
N.B. This command returns two lines split by a carriage return line feed and terminated by a carriage
return line feed. This command requires that the sensor has been stopped (see ‘K’ command).
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Production Data, Revision 4.7, 6 April 2021
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ExplorIR®-M
Small Footprint Low Power CO2 Sensor
CONNECTION DIAGRAM FOR UART INTERFACE
SENSOR SLAVE
Rx_IN
Tx_OUT
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UART MASTER
Tx_OUT
Rx_IN
Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
IMPORTANT NOTICE
Gas Sensing Solutions Ltd. (GSS) products and services are sold subject to GSS’s terms and conditions of sale,
delivery and payment supplied at the time of order acknowledgement. GSS warrants performance of its
products to the specifications in effect at the date of shipment. GSS reserves the right to make changes to its
products and specifications or to discontinue any product or service without notice.
Customers should therefore obtain the latest version of relevant information from GSS to verify that the
information is current. Testing and other quality control techniques are utilised to the extent GSS deems
necessary to support its warranty. Specific testing of all parameters of each device is not necessarily
performed unless required by law or regulation. In order to minimise risks associated with customer
applications, the customer must use adequate design and operating safeguards to minimise inherent or
procedural hazards. GSS is not liable for applications assistance or customer product design. The customer is
solely responsible for its selection and use of GSS products. GSS is not liable for such selection or use nor for
use of any circuitry other than circuitry entirely embodied in a GSS product.
GSS products are not intended for use in life support systems, appliances, nuclear systems or systems where
malfunction can reasonably be expected to result in personal injury, death or severe property or
environmental damage. Any use of products by the customer for such purposes is at the customer’s own risk.
GSS does not grant any licence (express or implied) under any patent right, copyright, mask work right or other
intellectual property right of GSS covering or relating to any combination, machine, or process in which its
products or services might be or are used. Any provision or publication of any third party’s products or
services does not constitute GSS’s approval, licence, warranty or endorsement thereof. Any third party trademarks contained in this document belong to the respective third-party owner.
Reproduction of information from GSS datasheets is permissible only if reproduction is without alteration and
is accompanied by all associated copyright, proprietary and other notices (including this notice) and
conditions. GSS is not liable for any unauthorised alteration of such information or for any reliance placed
thereon.
Any representations made, warranties given, and/or liabilities accepted by any person which differ from those
contained in this datasheet or in GSS’s standard terms and conditions of sale, delivery and payment are made,
given and/or accepted at that person’s own risk. GSS is not liable for any such representations, warranties or
liabilities or for any reliance placed thereon by any person.
ADDRESS
Gas Sensing Solutions Ltd.
Grayshill Road
Cumbernauld
G68 9HQ
United Kingdom
Gas Sensing Solutions Ltd.
Page | 27
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Production Data, Revision 4.7, 6 April 2021
Copyright © 2020 Gas Sensing Solutions Ltd.
ExplorIR®-M
Small Footprint Low Power CO2 Sensor
REVISION HISTORY
DATE
05/03/2020
05/05/2020
11/06/2020
18/11/2020
07/01/2021
19/01/2021
01/02/2021
06/04/2021
RELEASE
4.0
4.1
4.2
4.3
4.4
4.5
4.6
4.7
DESCRIPTION OF CHANGES
First revision
Changed auto-zero explanation
Absolute maximum ratings
Absolute maximum ratings
Added package pin length tolerance
Added ‘.’ COMMAND (0x2E)
ABSOLUTE MAXIMUM RATINGS
Updated response time
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PAGES
All
All
P.6
P.7
P.5
P.18
P.6
P.7
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