SDP616

SDP6x6 (SDP606/616) Differential Pressure Sensor with Power Saving Mode       Automatic power saving mode when idle Accuracy better than 0.2% FS near zero Digital output (I2C) Excellent repeatability, even below 10 Pa Calibrated and temperature compensated Excellent long-term stability Product Summary The SDP6x6 sensor is a special version in Sensirion’s SDP600 series of digital differential pressure sensors designed for high-volume applications. Just like all other SDP600 series sensors, the SDP6x6 measures the pressure of air and non-aggressive gases with superb accuracy and no offset drift. Additionally the SDP6x6 switches off power consuming functions in the sensor after a measurement and so saves more than 99.9% power during idle mode. The outstanding performance of these sensors is based on Sensirion’s patented CMOSens® sensor technology, which combines the sensor element, signal processing and digital calibration on a tiny microchip. The differential pressure is measured by a thermal sensor element using flow-through technology. Compared with membranebased sensors, the SDP6x6 features an extended dynamic range, better long-term stability, and improved repeatability, especially near zero. The SDP6x6 operates from a 3V supply voltage and features a digital 2-wire interface, which makes it easy to connect directly to a microprocessor. The signal is internally linearized and temperature compensated. The well-proven CMOS technology is perfectly suited for high-quality mass production and is the ideal choice for demanding and cost-sensitive OEM applications. Power Saving Mode Sensor chip The SDP6x6 automatically switches off the heater, ADC and other chip functions after a measurement in order to save power. During the power saving mode only the I2C interface will remain active and will trigger the rest of the sensor on the next measurement command. The SDP6x6 is intended for applications where differential pressure measurements are only required once in a while and measurement speed is not required. The SDP6x6 features the fourth-generation silicon sensor chip. In addition to a thermal mass flow sensor element, the chip contains an amplifier, A/D converter, EEPROM memory, digital signal processing circuitry, and interface. The highly sensitive chip requires only a minuscule amount of gas flow through the sensor. Applications OEM options  Medical  HVAC  Process automation A variety of custom options can be implemented for highvolume OEM applications. Ask us for more information. www.sensirion.com Version 1 – June 2015 1/10 1. Sensor Performance 1.1 Physical specifications1 Parameter SDP606 SDP616 Short Description Differential Pressure Sensor with Power Saving Mode Calibrated range – 500 Pa to + 500 Pa (± 2.0 in. H2O) Temperature-compensation yes Resolution 16bit Zero point accuracy2,3 0.2 Pa Span accuracy2,3 3% of reading Zero point repeatability2,3 0.1 Pa Span repeatability2,3 0.5% of reading Offset shift due to temperature variation (less than resolution) None Span shift due to temperature variation < 0.5% of reading per 10°C Offset stability < 0.1 Pa/year Response time 90 ms typical Time between measurements > 900 ms (shorter measurement intervals will affect accuracy of measurement results) 1 All sensor specifications are valid at 25°C with Vdd = 3 V and absolute pressure = 966 mbar and at most one measurement per second. Includes repeatability and hysteresis. 3 Total accuracy/repeatability is a sum of zero-point and span accuracy/repeatability. 2 www.sensirion.com Version 1 – June 2015 2/10 1.2 Ambient conditions Parameter Calibrated for4 Media compatibility Calibrated temperature range Operating temperature Storage temperature4 Position sensitivity 1.3 SDP606 / SDP616 Air, N2 Air, N2, O2 -20 °C to +80 °C -20 °C to +80 °C -40 °C to +80 °C Less than repeatability error Materials Parameter Wetted materials REACH, RoHS, SDP606 / SDP616 PBT (polybutylene terephthalate), glass (silicon nitride, silicon oxide), silicon, gold, FR4, silicone as static sealing, epoxy, copper alloy, lead-free solder REACH and RoHS compliant 2. Electrical Specifications Parameter Operating voltage Current drain while measuring SDP606 / SDP616 2.7 – 3.3 V (A supply voltage of 3 V is recommended) < 5 mA typical in operation Interface Bus clock frequency < 1 A Digital 2-wire interface (I2C) 100 kHz typical, 400 kHz max. Default I2C address 64 (binary: 1000 000) Current drain in sleep mode Scale factor Scale factor to Pascal Scale factor to alternative units5 60 Pa-1 6’000 mbar-1 413’686 psi-1 14’945 (inch H2O)-1 Contact Sensirion for information about other gases, wider calibrated temperature ranges and higher storage temperatures. Instead of the standard scale factor (to get the physical value in Pa), the sensor output may be divided by alternative scale factors to receive the physical value in another unit. 4 5 www.sensirion.com Version 1 – June 2015 3/10 3. Interface Specifications The serial interface of the SDP6x6 is compatible with I2C interfaces. For detailed specifications of the I2C protocol, see The I2C Bus Specification (source: NXP). 3.1 Transmission STOP Condition (P): The STOP condition is a unique situation on the bus created by the master, indicating to the slaves the end of a transmission sequence (the bus is considered free after a STOP). I2C Transmission Stop Condition SDA Interface connection – external components Bi-directional bus lines are implemented by the devices (master and slave) using open-drain output stages and a pull-up resistor connected to the positive supply voltage. The recommended pull-up resistor value depends on the system setup (capacitance of the circuit or cable and bus clock frequency). In most cases, 10 kΩ is a reasonable choice. The capacitive loads on SDA and SCL line have to be the same. It is important to avoid asymmetric capacitive loads. I2C Transmission Start Condition VDD master Rp Rp SCL P STOP condition A LOW to HIGH transition on the SDA line while SCL is HIGH. Acknowledge (ACK) / Not Acknowledge (NACK): Each byte (8 bits) transmitted over the I2C bus is followed by an acknowledge condition from the receiver. This means that after the master pulls SCL low to complete the transmission of the 8th bit, SDA will be pulled low by the receiver during the 9th bit time. If after transmission of the 8th bit the receiver does not pull the SDA line low, this is considered to be a NACK condition. If an ACK is missing during a slave to master transmission, the slave aborts the transmission and goes into idle mode. slave (SDP600) SDA I2C Acknowledge / Not Acknowledge SCL Both bus lines, SDA and SCL, are bi-directional and therefore require an external pull-up resistor. not acknowledge SDA acknowledge 3.2 I2C Address SCL The I2C address consists of a 7-digit binary value. By default, the I2C address is set to 64 (binary: 1000 000). The address is always followed by a write bit (0) or read bit (1). The default hexadecimal I2C header for read access to the sensor is therefore h81. 3.3 Transfer sequences Transmission START Condition (S): The START condition is a unique situation on the bus created by the master, indicating to the slaves the beginning of a transmission sequence (the bus is considered busy after a START). I2C Transmission Start Condition R/_W ACK D7 Each byte is followed by an acknowledge or a not acknowledge, generated by the receiver Handshake procedure (Hold Master): In a master-slave system, the master dictates when the slaves will receive or transmit data. However, in some situations a slave device may need time to store received data or prepare data to be transmitted. Therefore, a handshake procedure is required to allow the slave to indicate termination of internal processing. I2C Hold Master SCL R/_W ACK D7 Hold master: SCK line pulled LOW S START condition A HIGH to LOW transition on the SDA line while SCL is HIGH www.sensirion.com ACK SDA SDA SCL D0 D0 ACK data ready: SCK line released After the SCL pulse for the acknowledge signal, the sensor (slave) can pull down the SCL line to force the master into a wait state. By releasing the SCL line, the sensor indicates that its internal processing is completed and transmission can resume. (The bold lines indicate that the sensor controls the SDA/SCL lines.) Version 1 – June 2015 4/10 A command is represented by an 8-bit command code. The data direction may not change after the command byte, since the R/_W bit of the preceding I2C header has already determined the direction to be master-to-slave. In order to execute commands in Read mode using I2C, the following principle is used. On successful (acknowledged) receipt of a command byte, the sensor stores the command nibble internally. The Read mode of this command is then invoked by initiating an I2C data transfer sequence with R/_W = 1. If a correctly addressed sensor recognizes a valid command and access to this command is granted, it responds by pulling down the SDA line during the subsequent SCL pulse for the acknowledge signal (ACK). Otherwise it leaves the SDA line unasserted (NACK). The two most important commands are described in this data sheet, and the data transfer sequences are specified. Contact Sensirion for advanced sensor options. Measurement triggering Each individual measurement is triggered by a separate read operation. Note that two transfer sequences are needed to perform a measurement. First write command byte hF1 (trigger measurement) to the sensor, and then execute a read operation to trigger the measurement and retrieve the flow or differential pressure information. On receipt of a header with R/_W=1, the sensor generates the Hold Master condition on the bus until the first measurement is completed, which takes around 70ms. After the Hold Master condition is released, the master can read the result as two consecutive bytes. A CRC byte follows if the master continues clocking the SCL line after www.sensirion.com 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1 1 1 1 0 0 0 1 W I2CAdr 1 2 3 4 5 6 7 8 S 1 0 0 0 0 0 0 1 Command 9 ACK 2 Hold Master R I2CAdr LSByte MeasData Check Byte ACK MSByte MeasData ACK 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 P Hatched areas indicate that the sensor controls the SDA line. Note that the first measurement result after reset is not valid. 4.2 4. Command Set and Data Transfer Sequences 4.1 1 S 1 0 0 0 0 0 0 0 Soft reset This command forces a sensor reset without switching the power off and on again. On receipt of this command, the sensor reinitializes the control/status register contents from the EEPROM and starts operating according to these settings. I2C Soft Reset 8-bit command code: hFE Command: Soft reset 1 2 3 4 5 6 7 8 S 1 0 0 0 0 0 0 0 I2CAdr 4.3 W 9 10 11 12 13 14 15 16 17 18 1 1 1 1 1 1 1 0 ACK The value of the R/_W bit in the header determines the data direction for the rest of the data transfer sequence. If R/_W = 0 (WRITE) the direction remains master-to-slave, while if R/_W = 1 (READ) the direction changes to slaveto-master after the header byte. 8-bit command code: hF1 Command: Trigger differential pressure measurement ACK A data transfer sequence is initiated by the master generating the Start condition (S) and sending a header byte. The I2C header consists of the 7-bit I2C device address and the data direction bit (R/_W). I2C Measurement ACK Data is transferred in byte packets in the I2C protocol, which means in 8-bit frames. Each byte is followed by an acknowledge bit. Data is transferred with the most significant bit (MSB) first. the second result byte. The sensor checks whether the master sends an acknowledge after each byte and aborts the transmission if it does not. ACK Data transfer format ACK 3.4 system reboot Command CRC-8 Redundant Data Transmission Cyclic redundancy checking (CRC) is a popular technique used for error detection in data transmission. The transmitter appends an n-bit checksum to the actual data sequence. The checksum holds redundant information about the data sequence and allows the receiver to detect transmission errors. The computed checksum can be regarded as the remainder of a polynomial division, where the dividend is the binary polynomial defined by the data sequence and the divisor is a “generator polynomial”. The sensor implements the CRC-8 standard based on the generator polynomial x8 + x5 + x4 +1. Note that CRC protection is only used for date transmitted from the slave to the master. For details regarding cyclic redundancy checking, please refer to the relevant literature. Version 1 – June 2015 5/10 5. Conversion to Physical Values 5.1 6. OEM Options Signal scaling and physical unit The calibrated signal read from the sensor is a signed INTEGER number (two's complement number). The INTEGER value can be converted to the physical value by dividing it by the scale factor (pressure = sensor output  scale factor). The scale factor is specified in Section Fehler! Verweisquelle konnte nicht gefunden werden.. 5.2 A variety of custom options can potentially be implemented for high-volume OEM applications. Contact Sensirion for more information. Temperature compensation The SDP6x6 features digital temperature compensation. The temperature is measured on the CMOSens® chip by an on-chip temperature sensor. This data is fed to a compensation circuit that is also integrated on the CMOSens® sensor chip. No external temperature compensation is necessary. 5.3 Altitude correction The SDP6x6 achieves its unsurpassed performance by using a dynamic measurement principle. The applied differential pressure forces a small flow of gas through the sensor, which is measured by the flow sensor element. As a result, any variation in gas density affects the sensor reading. While temperature effects are compensated internally, variations in atmospheric pressure (elevation above sea level) can be compensated by a correction factor according to the following formula: DPeff = DPsensor  (Pcal / Pamb) DPeff: Effective differential pressure DPsensor: Differential pressure indicated by the sensor Pcal: Absolute pressure at calibration (966 mbar) Pamb: Actual ambient absolute pressure. Altitude correction factors: Altitude Ambient pressure (Pamb) Correction factor [meters] [mbar] (Pcal / Pamb) 0 250 425 500 750 1500 2250 3000 1013 984 966 958 925 842 766 697 0.95 0.98 1.00 1.01 1.04 1.15 1.26 1.38 Example: At 750 m above sea level and a sensor reading of 40 Pa, the effective differential pressure is 41.8 Pa. www.sensirion.com Version 1 – June 2015 6/10 7.4 7. Mechanical Specifications 7.1 SDP616 – Tube connection Mechanical concept The SDP6x6 is designed for through-hole technology and can be wave-soldered or hand-soldered to a PCB.   7.2 The SDP606 can be directly connected to a manifold using two O-rings. The SDP616 has ports for connecting standardsize plastic tubes. Mechanical characteristics Parameter PCB attachment Allowable overpressure Rated burst pressure Gas flow through sensor Weight Protection rating 7.3 Clip-in and hand or wave soldering. Additional mechanical attachment depending on force requirements 1 bar (100 kPa, 400 inches H2O) > 5 bar Figure 3: SDP616 version with ports for tube connection. All dimensions are in mm. < 150 ml/min