SP1202S01RB-PCB

December 2009 Rev – 1.4 Differential Pressure Sensor Board SP1202S01RB Users' Guide © 2009 National Semiconductor Corporation. 1 http://www.national.com Table of Contents 1.0 Introduction............................................................................................................................ 3 2.0 Board Assembly .................................................................................................................... 3 3.0 Quick Start............................................................................................................................. 3 4.0 Functional Description........................................................................................................... 4 4.1 Operational Modes................................................................................................... 4 4.1.1 The Computer Mode ................................................................................ 4 4.1.2 The Stand-Alone Mode ............................................................................ 4 4.2 Signal Conditioning Circuitry .................................................................................... 4 4.2.1 The Amplifier ............................................................................................ 4 4.2.1.1 Amplifier Gain Customization................................................... 4 4.2.1.2 Using Sensors with a Gain Resistor ........................................ 4 4.2.2 Sensor Drive ............................................................................................ 5 4.2.2.1 Sensor Voltage Drive ............................................................... 5 4.2.2.2 Sensor Current Drive ............................................................... 5 4.2.3 Offset Correction ...................................................................................... 5 4.2.4 Non-Linearity Correction .......................................................................... 5 4.2.5 Level Shifting............................................................................................ 5 4.3 Power Supply ........................................................................................................... 5 4.3.1 +3.3V up to +12V Operation .................................................................... 5 4.4 ADC Reference Circuitry.......................................................................................... 5 4.5 ADC clock................................................................................................................. 6 4.6 Digital Data Output. .................................................................................................. 6 4.7 Power Requirements................................................................................................ 6 5.0 Installing and Using the Sensor Path Pressure Sensor Board ............................................. 6 5.1 Board Set-up ............................................................................................................ 6 5.2 Quick Check of Analog Functions............................................................................ 6 5.3 Quick Check of Software and Computer Interface Operation ................................. 6 5.4 Troubleshooting ....................................................................................................... 7 6.0 Evaluation Board Specifications............................................................................................ 7 7.0 Example Hardware Schematic.............................................................................................. 8 8.0 Differential Pressure Sensor Board Example Bill of Materials.............................................. 9 Summary Tables of Test Points and Connectors ....................................................................... 10 Summary Tables of Test Points and Connectors (cont'd) .......................................................... 11 2 http://www.national.com 1.0 Introduction 2.0 Board Assembly The Differential Pressure Sensor Board (SP1202S01RB), along with the Sensor Signal Path Control Panel (Sensor Panel) software and SPUSI2 USB Interface Dongle, are designed to ease the design of circuits using various pressure sensors and load cells with National Semiconductor's amplifiers and Analog-to-Digital converters (ADCs). Use the WEBENCH® Pressure Sensor Designer tool to determine appropriate ICs and passive components to achieve your signal path requirements: http://webench.national.com/webench5/sensors/pres sure This Differential Pressure Sensor Board comes as a bare board that must be assembled. Refer to the example Bill of Materials for a description of component values, to Figure 1 for major component placement and to Figure 2 for the Board schematic. See Figure 1 for component placement and Figure 2 for example board schematic. The differential output pressure sensor is connected to header J1 The differential voltage at the sensor output (the voltage at TP1 relative to the voltage at TP2) is digitized and can be captured and displayed on the computer monitor with the accompanying Sensor Panel software, which operates under Microsoft Windows XP. The amplified differential voltage may be measured at TP3 relative to ground. The software can provide gain and offset correction for the entire circuit, including the sensor. 3.0 Quick Start Refer to Figure 1 for locations of test points and major components. This Quick Start procedure provides 5V excitation for the sensor. 1. Place the J2 jumper across pins 1 & 2. 2. Place the J3 jumper across pins 2 & 3. 3. Connect the Differential Pressure Sensor Board to a SPUSI2 board via 14-pin header J4 and connect a USB cable between the SPUSI2 board and a PC USB port. Red LEDs D2 on the differential Pressure Sensor Board and D1 on the SPUSI2 board should come on if the PC is on. 4. Connect the pressure sensor to 6-pin connector J1 of the board. 5. If not already installed, install the Sensor Panel software on the PC. Run the software. Figure 1. Component and Test Point Locations 3 http://www.national.com 4.0 Functional Description The Differential Pressure Sensor Board component and test point locations are shown in Figure 1. The board schematic is shown in Figure 2. 4.1 Operational Modes This board may be use in one of two modes: the Computer Mode using the SPUSI2 USB Interface Dongle or the Stand-Alone Mode without the use of the SPUSI2 USB Interface Dongle and a PC. 4.1.1 The Computer Mode The board is intended for use in the Computer Mode, where a SPUSI2 board is used with it and the SPUSI2 board is connected to a PC via a USB port. Power to both boards is provided via USB. 4.1.2 The Stand-Alone Mode The Stand-Alone Mode does not use the SPUSI2 board to capture data and upload it to a PC. To use the board this way, the user must provide +5V at pin 14 of header J4 as well as provide ADC clock and Chip Select signals to the ADC at pins 3 and 1, respectively, of J4. ADC data output is available at pin 5 of J4. Test Points TP10, TP11 and TP12 may also be used to insert/read these signals. The range of frequencies for the ADC clock is 1 MHz to 4 MHz. The CS rate can be as low as desired, but no faster than 17 times the ADC clock rate. The overall gain from the sensor to the ADC input, then, is Overall Gain = (1 + 2 * RF1 / RG1) * RB1 / RA1. Because of the way the difference amplifier is connected to the final amplifier, the overall gain is positive, hence the negative sign of the final amplifier is not included in the overall gain equation. 4.2.1.1 Amplifier Gain Customization Customization of the circuit consists primarily of adjusting the amplifier gain. As indicated above, the overall gain from the sensor to the ADC input is defined as Overall Gain = AV = (1 + 2 * RF1 / RG1) * RB1 / RA1. Of course, this assumes that RF1 = RF2, RA1 = RA2 and RB1 = RB2. Rearranging the above equation and solving for AV results in RG1 = (2 * RF1 * RB1) / (AV * RA1 - RB1). However, resistor tolerance can cause the ADC to reach full scale early. The solution to this is to assume RF1 and RB1 tolerance to be high and the tolerance of RA1 and RG1 to be low. This correctly implies that the required nominal value of RG1 should be a minimum of RG1 = [ (2 * H * RF1 * RB1) / (AV * L * RA1 - H * RB1) ]. Where H = 1 + resistor tolerance and L = 1 - resistor tolerance 4.2 Signal Conditioning Circuitry The sensor output voltage is found at TP1 relative to TP2. This voltage is amplified and digitized by U5, an ADC. The full-scale value of this voltage after amplification will depend upon the maximum sensor output and the component values. This amplified voltage is presented to the ADC (U5), whose output is at header J4. 4.2.1 The Amplifier Most pressure sensors are used with only a positive output at the (+) terminal with respect to the (-) terminal and this is the intended use of this board. If an offset is desired because the sensor (+) terminal could be negative with respect to its (-) terminal, resistor RB2 should be returned to a positive potential equal to half of the ADC reference voltage, found at test point TP13. Amplifiers U2A and U2B form an difference amplifier which amplifies the differential output of the bridge transducer. The gain of the difference amplifier, assuming RF1 = RF2, is the classic Differential Gain = 1 + 2 * RF1 / RG1. The differential output is converted to a single-ended signal with amplifier U3. The gain of the U3 circuit, assuming RB1 = RB2 and RA1 = RA2, is the wellknown Single-Ended Gain = – RB1 / RA1. 4 For example, for a resistor tolerance 1%, H = 1.01 and L = 0.99. 4.2.1.2 Using Sensors with a Gain Resistor Sensor output can vary by up to 50% from nominal, in some cases. Some sensors have internal gain resistors to precisely set the full scale output of the sensor. To take advantage of this, connect the gain resistor of the sensor between pins 3 and 4 of J1. Consult the sensor data sheet to determine the recommended value of RF1 and RF2, which is most often 100k-Ohms. The data sheet will indicate the full scale output level after the differential amplifier. The second amplifier stage should have a gain such that the differential amplifier full scale output multiplied by this gain will yield the ADC reference voltage. The gain of this stage, then, should be Gain = ADC VREF / Diff Out. For example, one sensor calls for RF1 = RF2 = 100kOhms for a differential output of 3.012V. The ADC reference voltage is 4.096V, therefore, the second stage gain should be Gain = 4.096 / 3.012 = 1.36. Setting RB1 = RB2 = 1.33k-Ohms and setting RA1 = RA2 = 1 k Ohms, provides a gain of 1.33 will provide a full scale input voltage to the ADC of 4.006V, http://www.national.com leaving a little headroom for resistor tolerances. Software adjustment of gain can then do a minor correction to precisely adjust the reading. http://www.national.com/analog/webench/sensors/sp usi2 4.2.2 Sensor Drive The sensor may be driven with either a voltage source or a current source. The default setup is for voltage drive of the sensor at +5V Because most sensors today use a small part of their full pressure range, they are very linear and there is no need for linearity correction. Consequently, there is not provision for linearity correction on this board. 4.2.2.1 Sensor Voltage Drive 4.2.5 Level Shifting For +5V voltage drive of the sensor, place the jumper on J2 across pins 1 and 2. This is the default setting. For voltage drive of the sensor with any other potential, place the jumper on J2 across pins 2 and 3 and provide a voltage source at TP15 that is at least 1.5 Volts greater than the desired bridge voltage. However, never exceed 12V at P1. Resistors RC1 through RC5 (lower left of Figure 2) should be set as follows, where VBR is the desired sensor drive voltage and VADC is the ADC supply voltage at TP13: Level shifting is sometimes used to raise the amplifier output slightly when no negative supply voltage is used in the system. This allows the accurate measurement of pressures or forces at and near zero. This board does not allow for this level shifting.      Set RC1 to a convenient value less than about 5k-Ohms Set RC2 = VBR * RC1 / VADC - RC1 Set RC3 to 0 Ohms Remove RC4 and leave open Set RC5 to 0 Ohms 4.2.2.2 Sensor Current Drive The current source provided on this board is a modified Howland Current pump, which performs quite well, but the output current does have some sensitivity to the load impedance. 4.2.4 Non-Linearity Correction 4.3 Power Supply In the Computer Mode, power to this board is supplied through header J14 and ultimately from the host PC via USB. In most cases, the only voltage needed for the Pressure Sensor board is the +5V from the USB connection. Diode D1 provides protection against reverse polarity in the Stand-Alone mode where an external supply is used. When the bridge drive circuit using U1 is used, a separate supply voltage is required to be provided at TP15. The supply voltage source for the ADC (VADC on the schematic) is selected with JP3 to be either the 4.1V from U4, or +5V from J14. The board is intended to be operated at +5V. However the board is capable of operation from +3.3V up to +12V. 4.3.1 +3.3V up to +12V Operation The sensor may be provided with a current drive by selecting appropriate values for resistors RC1 through RC5 and providing an appropriate voltage at TP15. The values in the schematic of Figure 2 are for a current drive of 1.5 mA. In the Computer Mode, install a 6x2 header, lining up with pin 1 marker and leaving pins 13 & 14 unconnected. Alternatively, break 2 pins (13 & 14) off the 7x2 header supplied in the Build-It kit. In StandAlone Mode no board modifications are required. For other current values, the WEBENCH Sensor Designer tool will provide appropriate component values. Set ADC supply to output of voltage reference U5 by placing the J3 jumper across pins 2 & 3. Use TP14 to externally power-up board from +3.3V up to +12V. This same voltage will power bridge when J2 jumper is placed across pins 1 & 2. If greater voltage is necessary to power bridge leave J2 jumper open and use TP4 to power bridge with another external power supply. 4.2.3 Offset Correction If offset correction is required, two axial resistors, RX1 & RX2 can be added as shown in the schematic of Figure 2 to provide required offset. RX1 can be placed from RB2 to VADC at TP13. RX2 can be placed from RB1 to GND at TPG1. The WEBENCH Sensor Designer tool will provide appropriate RX resistor values to achieve your offset requirements. If you have modified the board for offset correction you must use the Sensor Panel software calibration feature to capture the correct transfer function of your sensor. Note if your board has offset correction the Amplifier Input field in the Sensor Panel software will no longer be correct. For more details regarding the Sensor Panel software see the Manual at: 5 If board is operated at +5.25V and below you may also set ADC supply to board supply by placing the J3 jumper across pins 1 & 2. 4.4 ADC Reference Circuitry The single-ended ADC121S021 uses its supply voltage as its reference, so it is important that its supply voltage be stable and quiet. A 4.1V reference voltage is provided by U4, an accurate LM4120-4.1. http://www.national.com 4.5 ADC clock The ADC clock signal is provided external to the board at header J4. The frequency of this clock should be in the range of 1 MHz to 4 MHz. A CS (Chip Select) signal is also required at J4. See the ADC data sheet for timing requirements. 4.6 Digital Data Output. The digital output data from the ADC is available at 14-pin header J4. All digital signals to and from the ADC are present at this connector socket. 4.7 Power Requirements Voltage and current requirements for the Differential Pressure Sensor Board are:    Pin 14 of J4: +5.0V at 30 mA Pins 2 and 4 of J4: Ground TP15: Depends upon sensor 2. Be sure all jumpers are in place per Table 2, below. 3. Connect the sensor to J1 with the top of the bridge connected to pin 1 and the bottom of the bridge to pin 6. Connect the +output of the sensor to pin 2 and the -output of the sensor to pin 5. 4. Connect a USB cable to the SPUSI2 board and a PC. 5. Confirm that Red LED D1 on the Differential Pressure Sensor board is on, indicating the presence of power to the board. 6. If the sensor contains a gain setting resistor, connect the sensor gain set resistor across pins 3 and 4 of J1. Resistors RF1, RF2, RA1, RA2, RB1 and RB2 may have to be adjusted as previously described in Section 4.2.1.2. Table 2 - Jumper Default Positions Pins Jumper FUNCTION Shorted 5.0 Installing and Using the Sensor Path Pressure Sensor Board This Differential Pressure Sensor board requires power as described above. The pressure sensor should be connected to J1 pins 2 and 5. It may be necessary to change the value of RG1 to provide appropriate gain for the particular sensor used. To determine the correct value of RG1 for a given application, first determine the required overall gain: Total Gain = 5000 / Sensor FS (mV). Then determine the correct value of RG1 according to the discussion in Section 4.2.1.1. Alternatively, with RF1 = RF2 = 10k-Ohms, RB1 = RB2 = 2k-Ohms and RA1 = RA2 - 1k-Ohms, with all of these resistors a 1% tolerance RG1 may be set as indicated in Table 1. (Refer to Section 4.2.1.1.) Table 1 - Selecting RG1 Sensor Sensitivity (mV/V) Sensor Excitation (Volts) RG1 Value (Ohms) 10 5 511 10 10 1,050 25 5 1,330 25 10 2,870 50 5 2,870 50 10 6,650 100 5 6,650 100 10 20,000 J2 1-2 +5V Bridge Drive J3 2-3 4.1V ADC Reference 5.2 Quick Check of Analog Functions Refer to Figure 1 for locations of connectors and test points and jumpers on the board. If at any time the expected response is not obtained, see Section 5.4 on Troubleshooting. 1. 2. 3. 4. Perform steps 1 through 4 of Section 5.1. Check for 5.0V at TP14 and for 4.1V at TP13. Check for 5V at TP4 (top of sensor). Place a short between TP1 and TP2 and ground these two pins. Check for a voltage less than 70mV at TP3. Then remove the TP1 to TP2 short. 5. Apply a voltage of 2.5V at TP2 and 2.54V to TP1 and check for a voltage of between 2.5V and 4.0V at TP3. This completes the quick check of the analog portion of the evaluation board. 5.3 Quick Check of Software and Computer Interface Operation 5.1 Board Set-up Refer to Figure 1 for locations of connectors, test points and jumpers on the board. 1. Perform steps 1 through 4 of Section 5.1. 2. Run the SPC Program. 3. Place a short between TP1 and TP2 and ground these two pins and check the SPC software window for an output below 70 mV. 4. Remove the short between TP1 and TP2, but keep TP2 grounded. Apply a potential of half the sensor output to TP1 and check the SPC software window for an output of 2.0V and 2.1V. This completes the quick check of the software and computer interface. 1. Connect The Differential Pressure Sensor board to a SPUSI2 USB Interface Dongle. 6 http://www.national.com 5.4 Troubleshooting If there is no output from the board, check the following:  Be sure that the proper voltages and polarities are present at TP14 (+5V) and TP13 (+4.1V or +5V, as selected with J3).  Be sure there is a clock signal at TP10 when trying to capture data.  If using an actual sensor, be sure that the positive sensor output terminal is at J1 pin 2 and the negative sensor output terminal is at J1 pin 5. The voltage at TP1 should be equal to or greater than the voltage at TP2. If the amplifier output at TP3 can not be brought within 70 mV of ground, check the following:   Be sure there is a voltage at TP4 (top of sensor). Be sure that the voltage on pin 6 of J1 is zero, or that an appropriate resistor is present at R3 if the short across it is cut. If the ADC output is zero or a single code, check the following:  Be sure that the proper voltages and polarities are present at TP14 (+5V) and TP13 (+4.1V or +5V, as selected with J3).  Be sure that J4 is properly connected to a SPUSI2 USB Interface Dongle, and that there is a jumper on J3.  If using an actual sensor, be sure that the positive sensor output terminal is at J1 pin 2 and the negative sensor output terminal is at J1 pin 5. The voltage at TP1 should be equal to or greater than the voltage at TP2. 6.0 Evaluation Board Specifications Board Size: 2.6" x 2.5" (6.6 cm x 6.35 cm) Power Requirements: +5V (30mA) at J4 pin 14 7 http://www.national.com 7.0 Example Hardware Schematic 8 http://www.national.com 8.0 Differential Pressure Sensor Board Example Bill of Materials Item Qty Reference Part Source Kemet #C0805C331K5RACTU Digi-Key #399-1140-2-ND Vishay/Sprague #293D475X9016A2TE3 Digi-Key #718-1148-2-ND 1 4 CS1, C1, C2, C5 330pF, 50V, ±10%, 0805, X7R 2 4 C3, C6, C8, C15 4.7µF, 16V, Tant, ±20%, size "B" 3 6 C4, C7, C9, C10, C13, C14 4 1 C11 5 - C12 Not Stuffed 6 6 C16, C17 10pF, 100V, ±10%, 0805, NP0 7 1 D1 1N4001, DO-214AA / DO-214AC 8 1 D2 LED (RED) 9 1/6 J1 6-pin Header (0.1" - breakaway) 10 1 J2, J3 3-pin Header (0.1") 11 1 J4 2 x 7 Male Header RT/A (0.1") 12 2 RA1, RA2 1.00k, 1%, 1/10W, 0603 13 2 RB1, RB2 2.00k, 1%, 1/10W, 0603 14 2 RC1, RC3 49.9k, 1%, 1/10W, 0603 15 2 RC2, RC4 187, 1%, 1/10W, 0603 16 1 RC5 10.2, 1%, 1/10W, 0603 17 2 RF1, RF2 10.0k, 1%, 1/10W, 0603 18 1 RG1 1.07k, 1%, 1/10W, 0603 19 1 RS1 10, 5%, 1/10W, 0603 20 1 R3 0, 5%, 1/10W, 0603 21 1 R2 43, 1%, 1/10W, 0603 22 1 R7 1k, 5%, 1/10W, 0603 23 2 RX1, RX2 Selected by WEBENCH Note resistors are axial resistors. There is no footprint on board. 24 - TPG1, TPG2, TPG3 Not Stuffed n/a 25 - TP1, TP2, TP3, TP4, TP6, TP10, TP11, TP12, TP13, TP14, TP15 Not Stuffed n/a 27 1 U1 LMP7702/MSOP 28 1 U2 LMP7732MM/MSOP 29 1 U3 LMP7731/SOT 30 1 U4 LM4120AIM5-4.1 31 1 U5 ADC121S021CIMF/SOT23 32 1 PCB SP1202S01RB Yageo #CC0805KRX7R7BB104 Digi-Key #311-1142-2-ND Kemet #C0805C333K5RACTU 0.033µF, 50V, ±10%, 0805, X7R Digi-Key #399-1165-2-ND 0.1µF, 16V, ±10%, 0805, X7R 9 n/a AVX #08051A100KAT2A Digi-Key #478-3731-2-ND Micro Commercial #GS1A-TP Digi-Key #GS1A-TPTR-ND Lite-On #LTST-C930KAKT Digi-Key #160-1461-2-ND Molex #22-28-4363 Digi-Key #WM6536-ND Molex #68301-1009 Digi-Key #WM17443-ND Amp #87230-7 Digi-Key #A26599-ND Stackpole #RNCS 16 T9 1K 0.1% Digi-Key #RNCS16T91K0.1%ITR-ND Stackpole #RNCS 16 T9 2K 0.1% I Digi-Key #RNCS16T92K0.1%ITR-ND Susumu #RRG1608P-4992-B-T5 Digi-Key #RG16P49.9KBTR-ND Susumu #RG1608P-1870-B-T5 Digi-Key #RG1608P-1870-B-T5-ND Yageo #RT0603BRE0710R2L Digi-Key #RT0603BRE0710R2L-ND Bourns#CRT0603-BY-1002ELF Digi-Key #CRT0603-BY-1002ELFCT-ND Susumu #RG1608P-4530-B-T5 Digi-Key #RG16P453BCT-ND Rohm #MCR03EZPJ100 Digi-Key #RHM10GCT-ND Rohm #MCR03EZPJ000 Digi-Key #RHM0.0GCT-ND Susumu #RG1608P-433-B-T5 Digi-Key #RG16P43.0KBTR-ND Rohm #MCR03EZPJ152 Digi-Key #RHM1.5KGTR-ND Nat Semi #LMP7702MM/NOPB Digi-Key #LMP7702MMTR-ND Nat Semi #LMP7732MM/NOPB Digi-Key #LMP7732MMTR-ND Nat Semi #LMP7731MF/NOPB Digi-Key #LMP7731MFTR-ND Nat Semi #LM4120AIM5-4.1/NOPB Digi-Key #LM4120AIM5-4.1TR-ND Nat Semi #ADC121S021CIMF/NOPB Digi-Key #ADC121S021CIMFTR-ND Advanced Circuits http://www.national.com 10 http://www.national.com APPENDIX Summary Tables of Test Points and Connectors Test Points on the Differential Pressure Sensor Board Identifier TP 1 TP 2 TP 3 TP 4 TP 5 TP 6 TP 7 TP 8 TP 9 TP 10 TP 11 TP 12 TP 13 TP 14 TP 15 TPGx Name +IN -IN ADC IN+ BR_TOP +3V3 SCLK CSb DOUT VADC +5V V_EXT GND Function (+) Input from Bridge (-) Input from Bridge ADC +Input voltage Top of bridge Identifier not used +3.3V from SPUSI2 Board (not used on this board) Identifier not used Identifier not used Identifier not used SCLK input for ADC CSb input for ADC SDATA output from ADC ADC supply voltage/reference Overall supply for board from SPUSI2 Board Bridge Driver Amplifier supply voltage Ground J1 Connector - Sensor Interface Identifier J1-1 J1-2 J1-3 J1-4 J1-5 J1-6 Name Bridge "TOP" Bridge +Out Gain Resistor Gain Resistor Bridge -Out Bridge "BOT" Function Positive sensor excitation + Output from Sensor Gain Resistor Connection Gain Resistor Connection - Output from Sensor Ground or negative sensor excitation J2 Jumper - V_BR_SEL Shorted Positions 1-2 2-3 Results +5V Drive of Sensor U1 Drive of Sensor(Voltage or Current, depending upon components around U1 J3 Jumper - VADC_SEL Shorted Positions 1-2 2-3 Results +5V for ADC Supply and Reference Voltage +4.1V for ADC Supply and Reference Voltage 11 http://www.national.com Summary Tables of Test Points and Connectors (cont'd) J7 Connector - Connection to SPUSI2 Board J7 Pin Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Voltage or Signal CSb input to ADC Ground SCLK input to ADC Ground SDATA output from ADC no connection no connection no connection no connection no connection no connection no connection +3.3V from SPUSI2 USB Interface Dongle +5V from SPUSI2 USB Interface Dongle 12 http://www.national.com [Blank Page] 13 http://www.national.com The Differential Pressure Sensor Board is intended for product evaluation purposes only and is not intended for resale to end consumers, is not authorized for such use and is not designed for compliance with European EMC Directive 89/336/EEC. 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