September 2010 Rev – 1.0 High Resolution Differential Pressure Sensor Board SP1602S01RB Users' Guide © 2010 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 ............................................................................................ 4 4.2.2.1 Sensor Voltage Drive ............................................................... 4 4.2.2.2 Sensor Current Drive ............................................................... 4 4.2.3 Offset and Gain Correction ...................................................................... 5 4.2.4 Non-Linearity Correction .......................................................................... 5 4.2.5 Level Shifting............................................................................................ 5 4.3 Power Supply ........................................................................................................... 5 4.4 ADC Reference Circuitry.......................................................................................... 5 4.5 ADC clock................................................................................................................. 5 4.6 Digital Data Output. .................................................................................................. 5 4.7 Power Requirements................................................................................................ 5 5.0 Installing and Using the Sensor Path Pressure Sensor Board ............................................. 5 5.1 Board Set-up ............................................................................................................ 5 5.2 Quick Check of Analog Functions............................................................................ 5 5.3 Quick Check of Software and Computer Interface Operation ................................. 6 5.4 Troubleshooting ....................................................................................................... 6 6.0 Evaluation Board Specifications............................................................................................ 6 7.0 Example Hardware Schematic.............................................................................................. 7 8.0 Example Bill of Materials ....................................................................................................... 8 Summary Tables of Test Points and Connectors ....................................................................... 9 Summary Tables of Test Points and Connectors (cont'd) .......................................................... 10 2 http://www.national.com 1.0 Introduction 2.0 Board Assembly The High Resolution Differential Pressure Sensor Board (SP1602S01RB), along with the Sensor Signal Path Control Panel (Sensor Panel) software and SPUSI2 Data Capture Board, are designed to ease the design of circuits using various pressure sensors and load cells with National's amplifiers and Analogto-Digital converters (ADCs). Use the WEBENCH® Pressure Sensor Designer tool to determine appropriate ICs and passives to achieve your signal path requirements: http://www.national.com/analog/webench/sensors/pre ssure This High Resolution Differential Pressure Sensor Board comes as a kit with a bare board and components that must be assembled. Refer to the example Bill of Materials for a description of example component values, to Figure 1 for major component placement and to Figure 2 for the Example 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 TP5. 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 High Resolution 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 High Resolution 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 High Resolution Differential Pressure Sensor Board component and test point locations are shown in Figure 1. The example board schematic is shown in Figure 2. However, resistor tolerance can cause the ADC to reach full scale early. The solution to this is to assume RF1 tolerance to be high and the tolerance of RG1 to be low. This correctly implies that the required nominal value of RG1 should be a minimum of 4.1 Operational Modes RG1 = (2 * H * RF1) / (AV -1) . This board may be use in one of two modes: the Computer Mode using the SPUSI2 Data Capture Board or the Stand-Alone Mode without the use of the SPUSI2 Data Capture Board and a PC. Where H = 1 + resistor tolerance For example, for a resistor tolerance 1%, H = 1.01. 4.1.1 The Computer Mode 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, do not stuff resistor RG1 on the High Resolution Differential Pressure Sensor board and instead 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 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. 4.2.1.2 Using Sensors with a Gain Resistor 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. 4.2.2.1 Sensor Voltage Drive The sensor output voltage is found at TP1 relative to TP2. This voltage is amplified by amplifiers U2A, and U2B which form a difference amplifier. 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. 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 ADC_REF is the ADC reference voltage at TP13: 4.2.1 The Amplifier 4.2 Signal Conditioning Circuitry 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. Set RC1 to a convenient value less than about 5k-Ohms Set RC2 = VBR * RC1 / ADC_REF - RC1 Set RC3 to 0 Ohms Remove RC4 and leave open Set RC5 to 0 Ohms 4.2.2.2 Sensor Current Drive 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 Differential Gain = AV = 1 + 2 * RF1 / RG1. Of course, this assumes that RF1 = RF2. Rearranging the above equation and solving for AV results in RG1 = (2 * RF1) / (AV - 1). 4 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. 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 example schematic of Figure 2 are for a current drive of 1.5 mA. For other current values, the WEBENCH Sensor Designer tool will provide appropriate component values. http://www.national.com 5.0 Installing and Using the Sensor Path Pressure Sensor Board 4.2.3 Offset and Gain Correction The circuitry does not provide adjustment for offset voltages. However, the SPC software does allow for this correction. 4.2.4 Non-Linearity Correction 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. 4.2.5 Level Shifting 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. 4.3 Power Supply In the computer mode, power to this board is supplied through header J4 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-Along 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 ADC reference voltage source for the ADC (ADC_REF on the schematic) is selected with J3 to be either the 4.1V from U4, or +5V from J4. 4.4 ADC Reference Circuitry It is important that the reference of the differential ADC is stable and quiet. A 4.1V reference voltage is provided by U4, an accurate LM4120-4.1. 4.5 ADC clock This High Resolution 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 = ADC FS (mV) / Sensor FS (mV). Then determine the correct value of RG1 according to the discussion in Section 4.2.1.1. 5.1 Board Set-up Refer to Figure 1 for locations of connectors, test points and jumpers on the board. 1. Connect The High Resolution Differential Pressure Sensor board to a SPUSI2 Data Capture board. 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 High Resolution 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 and RF2 may have to be adjusted as previously described in Section 4.2.1.2. Table 2 - Jumper Default Positions Pins Jumper FUNCTION Shorted 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. 1-2 +5V Bridge Drive J3 2-3 4.1V ADC Reference 5.2 Quick Check of Analog Functions 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 High Resolution Differential Pressure Sensor Board are: J2 Pin 14 of J4: +5.0V at 30 mA Pins 2 and 4 of J4: Ground TP15: Depends upon sensor 5 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 tie these two pins to ADC_REF/2. Check for a voltage approximately equal to ADC_REF/2 at TP3. Then remove the TP1 to TP2 short. http://www.national.com This completes the quick check of the analog portion of the evaluation board. 5.3 Quick Check of Software and Computer Interface Operation 1. Perform steps 1 through 4 of Section 5.1. 2. Run the SPC Program. 3. Place a short between TP1 and TP2 and tie these two pins to ADC_REF/2 and check the SPC software window for an ADC input below 70 mV. This completes the quick check of the software and computer interface. 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. 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, and if that is not expected, 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 Data Capture Board, 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. 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 6 http://www.national.com 511, 0.1% 10, 0.1% 10, 0.1% 0.1% 10, 0.1uF 4.7 uF 0.1uF LM4120AIM5-4.1 7.0 Example Hardware Schematic 7 http://www.national.com 8.0 Example Bill of Materials Item Qty Reference Part Source 1 3 CS1,C1,C2 330pF,50V,±10%,0603,X7R 2 4 C3,C5,C6,C15, C19 4.7µF,16V,Tant,±20%,size"B" 3 5 C4,C7,C13,C14,C18 0.1µF,16V,±10%,0603,X7R 4 3 C10,C11 0.1µF,16V,±10%,1206,X7R R1,R3,C8,C12,C16,C17,D1 Not Stuffed 5 7 Kemet#C0603C331K5RACTU Digi-Key#399-1140-2-ND Vishay/Sprague#293D475X9016A2TE3 Digi-Key#718-1148-2-ND Yageo#CC0603KRX7R7BB104 Digi-Key#311-1088-2-ND Yageo#CC1206KRX7R9BB104 Digi-Key#311-1179-2-ND n/a 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#RMCF1/1649.9K1%R Digi-Key#RMCF1/1649.9K1%RTR-ND Stackpole#RMCF1/161871%R Digi-Key#RMCF1/161871%R-ND Stackpole#RMCF1/1610.21%R Digi-Key#RMCF1/1610.21%R-ND Stackpole#RMCF1/1610K1%G Digi-Key#RMCF1/1610K1%G-ND Stackpole#RMCF1/165111%R Digi-Key#RMCF1/165111%RTR-ND Stackpole#RMCF1/16101%R Digi-Key#RMCF1/16101%RTR-ND Susumu#RG1608P-433-B-T5 Digi-Key#RG16P43.0KBTR-ND Rohm#MCR03EZPJ152 Digi-Key#RHM1.5KGTR-ND 6 1 D2 LED(RED) 7 1/6 J1 6-pinHeader(0.1"-breakaway) 8 1 J2,J3 3-pinHeader(0.1") 9 1 J4 2x7MaleHeader(0.1") 10 2 RC1,RC3 49.9k,1%,1/10W,0603 11 2 RC2,RC4 187,1%,1/10W,0603 12 1 RC5 10.2,1%,1/10W,0603 13 2 RF1,RF2 10.0k,1%,1/10W,0603 14 1 RG1 511,1% 15 2 RS1,RS2 10,5%,1/10W,0603 16 1 R2 43,5%,1/10W,0603 17 1 R10 1k,5%,1/10W,0603 18 3 TPG1,TPG2,TPG3 Not Stuffed n/a 19 12 TP1,TP2,TP3,TP4,TP5,TP6,TP10, TP11,TP12,TP13,TP14,TP15 Not Stuffed n/a 20 1 U1 LMP7702/MSOP 21 1 U2 LMP7732MM/MSOP 22 1 U4 LM4120AIM5-4.1 1 U5 ADC161S626CIMM/MSOP 23 24 1 PCB 8 NatSemi#LMP7702MM/NOPB Digi-Key#LMP7702MMTR-ND NatSemi#LMP7732MM/NOPB Digi-Key#LMP7732MMTR-ND NatSemi#LM4120AIM5-4.1/NOPB Digi-Key#LM4120AIM5-4.1TR-ND NatSemi#ADC161S626CIMM/NOPB Digi-Key#ADC161S626CIMMTR-ND AdvancedCircuits http://www.national.com APPENDIX Summary Tables of Test Points and Connectors Test Points on the High Resolution 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 ADC IN+3V3 SCLK CSb DOUT VADC +5V V_EXT GND Function (+) Input from Bridge (-) Input from Bridge ADC +Input voltage Top of bridge ADC +Input voltage +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 9 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 Data Capture board +5V from SPUSI2 Data Capture board 10 http://www.national.com [Blank Page] 11 http://www.national.com The High Resolution 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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Tel: 81-3-5620-6175 Fax: 81-3-5620-6179 www.national.com National does not assume any responsibility for any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. 12 http://www.national.com