Sensor-Emulator-EVM System Reference Guide by Art Kay High-Precision Linear Products SBOA102A
Sensor-Emulator-EVM • Simplifies Development of Voltage Excited Bridge Sensor Signal Conditioning Systems • Provides Eleven Different Emulated Sensor Output Conditions • Provides Three Different Emulated Temperature Signals for Diode or Series Resistor Methods of Bridge Sensor Temperature Monitoring • Emulates Bridge Outputs - Cold Temp: 0%, 50%, 100% - Room Temp: 0%, 25%, 50%, 75%, 100% - Hot Temp: 0%, 50%, 100% • LED Indicators for Emulation at a Glance SBOA102A January 2005 Sensor-Emulator-EVM System R
Sensor Emulator EVM Table of Contents Pages 1.0 Introduction to the Sensor-Emulator-EVM………………………….………. 4-5 2.0 Overview Hardware Emulation of a Real World Sensor……………….……6-15 3.0 Changing the Programmable Range of the Emulator…………………….…17 4.0 Required Electrical connections……………………………………………….18-25 5.0 Configuring the Sensor-Emulator-EVM to Emulate a Real World Sensor…26-43 6.0 Schematic of Sensor-Emulator-EVM……………………..……………………44 7.0 Parts List for Sensor-Emulator-EVM………………………………………...
1.0 Introduction to The Sensor Emulator Q: A: Q: A: What is the sensor emulator? The sensor emulator is a design that uses rotary switches and potentiometers to emulate the operation of a resistive bridge sensor at discrete operating points, for voltage excitation applications. Why use the sensor emulator? Once the sensor emulator has been programmed, it allows the user to cycle through a set of sensor output conditions very quickly.
1.0 Introduction to The Sensor Emulator Q: A: Why not just use a precision voltage source to emulate a sensor? A precision voltage source is not affected by changing sensor excitation. Many sensor signal conditioning chips modulate the sensor excitation to compensate for sensor nonlinearity. In this case (and in the case of a ratiometric system), a precision voltage source would not work.
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Bridge Sensor Output Figure 2.1 Figure 2.2 Figure 2.1 is an example of a typical resistive bridge sensor with no applied stimulus. With no stimulus applied, the resistors ideally would be perfectly matched and the sensors’ output (VIN_DIF ) would be zero. Most practical sensors, however, will have some output resulting from resistor mismatch. The output signal with no applied stimulus is called offset. Figure 2.2 is an example of a typical resistive bridge sensor with full scale stimulus applied.
Drift and Nonlinearity with a Bridge Sensor Kbridge vs. pressure @Troom Bridge sensitivity vs. temp 4.0E-01 Kbridge, V/V or Vbridge@Vexc=1V 3.0E-01 2.5E-01 2.0E-01 Offset Span 1.5E-01 1.0E-01 Kbridge, V/V, or Vbridge@Vexc=1V 3.5E-01 3.5E-01 3.0E-01 2.5E-01 2.0E-01 1.5E-01 1.0E-01 5.0E-02 0.0E+00 5.0E-02 0 10 20 30 40 50 60 70 80 90 Pressure 0.0E+00 -50 0 50 100 150 Temp, degC Figure 2.3 Figure 2.4 An important aspect of pressure sensors is how they drift with temperature.
5.0V Emulating Bridge Sensor Outputs R8 R101 10k 10k 2.526V R102 200 ohm This is a simplified diagram of how the sensor emulator generates a bridge output voltage. The potentiometer R102 is adjusted to set the output voltage of the emulated bridge (Vin+ with respect to Vin-). The potentiometer R103 is used to make fine adjustments in the output value. R8 and R9 set a common mode voltage for the other leg of the bridge. R101 and R104 set the adjustable output range of the emulated bridge.
Emulating a Temperature Sensor with a Series Bridge Resistor (Rt- connected to the bottom of the bridge) VT Figure 2.6 V exc⋅ R T R T + R Bridge Figure 2.7 Figure 2.8 Figure 2.6 illustrates one method for monitoring the temperature of a real world bridge sensor. In this type of circuit the resistance of the bridge has a strong temperature coefficient.
Emulating a Temperature Sensor with a Series Bridge Resistor (Rt+ connected to the top of the bridge) VT Figure 2.9 V exc⋅ R T R T + R Bridge Figure 2.10 Figure 2.11 The sensor emulator circuit can also emulate the case where the temperature sense resistor is connected to the top of the bridge. This is done using an instrumentation amplifier to translate the voltage signal to be referenced to Vexc rather then ground. This mode of operation is selected by a jumper (JUMP1).
Diode Temperature Sensor Emulator Figure 2.12 Figure 2.13 Figure 2.14 Figure 2.12 illustrates another method for monitoring the temperature of a real world sensor. In this type of circuit a diode is placed in close thermal contact with the bridge and a constant current is driven through the diode. The diode voltage is a reasonably linear function with temperature (the slope is approximately -2mV / °C). The emulator circuit shown in Figure 2.
Emulation Case 1: Rt(Resistance in the Bottom of The Bridge) Rt- Temperature Signal Emulation Bridge Voltage Emulation Note that the output signals of the real world sensor and the emulator are the same. 1.101k VINP 1.1023k R2401 5.0V U1A + Adjusted to 1k R2402 R101 10k 50 2k R102 200 ohm U1b + 12.48mV VDIF = 12.4mV Adjusted to 50 R2403 Temperature Signal VT = 0.415V R103 Adjusted to 5 U1d + 10 ohm Output of Sensor Vin- to Signal Conditioning Chip 2.292V 100ohm R9 0.
Emulation Case 2: Rt+ (Resistance in the Top of The Bridge) Figure 2.16 This diagram illustrates how the emulator generates the bridge output and temperature signal for the circuit where the sense resistor is connected to the top of the bridge. Note how the output voltage of the temperature emulator (0.415V) is fed back to the bottom of the bridge emulator via the buffer circuit (U5 and U1c) to emulate the bridge excitation change due to Rt in series with the bridge in the real world.
Emulation Case 3: Diode Temperature Sensor with External Current Source Figure 2.17 This diagram illustrates how the emulator generates the bridge output and temperature signal for the diode temperature measurement. Note that in this case JUMP1 is set so that the bottom of the bridge emulator is at ground potential. Also note that this configuration requires an external current source to operate (in this example, 7µA).
Emulation Case 4: Diode Temperature Sensor with On-Board Voltage Reference Figure 2.17 This diagram illustrates how the emulator generates the bridge output and temperature signal for the diode temperature measurement. Note that in this case JUMP1 is set so that the bottom of the bridge emulator is at ground potential. Also note that this uses an on-board voltage reference (REF102) to set the diode voltage (JUMP2 selects this option).
3.0 Changing the Programmable Range of the Emulator Figure 3.1 illustrates how the range of the bridge emulator can be adjusted by putting a resistor in parallel with R101 and R104. This needs to be done for each channel of the emulator (11 channels x 2 resistors = 22 resistors total). The examples illustrates how the range is increased using a 1kΩ parallel resistor.
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Example of a Typical Engineering Bench Setup Using the Sensor Emulator This diagram illustrates an example of how the sensor emulator would be used in an engineering bench setup. The PGA309 is a programmable sensor signal conditioning chip. The Sensor-Emulator-EVM can be used in conjunction with the PGA309EVM to facilitate the development of a PGA309 application.
Note on the Buf_Temp Banana Jacks The Buf_Temp banana jacks are used to monitor the temperature signal with a DVM. It is important to monitor temperature at this point because the non-buffered temperature signal is a high impedance output, and the DVM can load this output.
Note on the Vin- and Vin+ Banana Jacks The Vin- and Vin+ banana jacks are used to monitor the sensor output signal with a DVM. The Vin banana jacks are connected to the Vin signal through a standard RC filter. This filter helps to reduce the coupling of noise (from ground loops) into the sensor output circuit, and into high gain sensor signal conditioner inputs.
These jumpers are not used in this mode. Any position is ok. SBOA102A January 2005 These three channels are used to set the temperature output signal in this mode. The diode channels are not used in this mode. Set the jumper JUMP1 to the position shown to connect the Rttemperature emulation. Sensor-Emulator-EVM System Reference Guide Set the jumper JUMP5 to the position shown to connect the Rt emulation.
These jumpers are not used in this mode. Any position is ok. SBOA102A January 2005 These three channels are used to set the temperature output signal in this mode. The diode channels are not used in this mode. Set the jumper JUMP1 to the position shown to connect the Rt+ temperature emulation. Sensor-Emulator-EVM System Reference Guide Set the jumper JUMP5 to the position shown to connect the Rt emulation.
These jumpers must be set to the position shown to allow for external current source connection. SBOA102A January 2005 These three channels are used to set the temperature output signal in this mode. The Rt channels are not used in this mode. Set the jumper JUMP1 to the position shown to connect the Diode temperature emulation. Sensor-Emulator-EVM System Reference Guide Set the jumper JUMP5 to the position shown to connect GND to the bottom of the bridge emulator.
These jumpers must be set to the position shown to allow the on board voltage reference to generate the emulated diode voltages. SBOA102A January 2005 These three channels are used to set the temperature output signal in this mode. The Rt channels are not used in this mode. Set the jumper JUMP1 to the position shown to connect the Diode temperature emulation. Sensor-Emulator-EVM System Reference Guide Set the jumper JUMP5 to the position shown to connect GND to the bottom of the bridge emulator.
5.0 Configuring the SensorEmulator-EVM to Emulate a Real World Sensor If the raw output of the sensor is not known, the generate_emu_values.xls spreadsheet (SBOC065, available for download at www.ti.com) can be used to translate the specifications of your bridge sensor and temperature sensor to system voltage levels. The spreadsheet contains five sections: 1. Offset and Span: Generates the bridge output voltages. 2. Diode Vo: Generates the temperature sensor output voltages for the diode method. 3.
Offset and Span: Generates the bridge output voltages from sensor specifications All the areas shown in light blue are either sensor specifications or system requirements. Enter these values and the spreadsheet will generate output voltage settings for each channel on the sensor emulator. The next several pages will show how the voltages listed in the spreadsheet are used to program the sensor emulator.
The sensor output at cold temperature and 0% of applied stimulus is emulated by this channel. The rotary switch S1 is used to select this channel. When the channel is selected, LED D101 will light to indicate that the correct channel is selected. Bridge Sensitivity v s Temp 4.5E-03 4.0E-03 3.5E-03 Kbridge, V/V 3.0E-03 2.5E-03 2.0E-03 offset 1.5E-03 span 1.0E-03 5.0E-04 0.0E+00 -5.0E-04 -1.
The sensor output at cold temperature and 100% of applied stimulus is emulated by this channel. The rotary switch S1 is used to select this channel. When the channel is selected, LED D103 will light to indicate that the correct channel is selected. Bridge Sensitivity v s Temp 4.5E-03 4.0E-03 3.5E-03 Kbridge, V/V 3.0E-03 2.5E-03 2.0E-03 offset 1.5E-03 span 1.0E-03 5.0E-04 0.0E+00 -5.0E-04 -1.
The sensor output at room temperature and 0% of applied stimulus is emulated by this channel. The rotary switch S1 is used to select this channel. When the channel is selected, LED D104 will light to indicate that the correct channel is selected. Kbridge vs. pressure @Troom 3.5E-03 Kbridge, V/V, or Vbridge@Vexc=1V 3.0E-03 2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04 0.0E+00 0 10 20 30 40 50 60 70 80 90 100 -5.0E-04 Pressure Emulate the nonlinearity of the curve at room temperature for four points.
The sensor output at room temperature and 25% of applied stimulus is emulated by this channel. The rotary switch S1 is used to select this channel. When the channel is selected, LED D105 will light to indicate that the correct channel is selected. Kbridge vs. pressure @Troom 3.5E-03 Kbridge, V/V, or Vbridge@Vexc=1V 3.0E-03 2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04 0.0E+00 0 10 20 30 40 50 60 70 80 90 100 -5.
The sensor output at room temperature and 50% of applied stimulus is emulated by this channel. The rotary switch S1 is used to select this channel. When the channel is selected, LED D106 will light to indicate that the correct channel is selected. Kbridge vs. pressure @Troom 3.5E-03 Kbridge, V/V, or Vbridge@Vexc=1V 3.0E-03 2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04 0.0E+00 0 10 20 30 40 50 60 70 80 90 100 -5.
The sensor output at room temperature and 75% of applied stimulus is emulated by this channel. The rotary switch S1 is used to select this channel. When the channel is selected, LED D107 will light to indicate that the correct channel is selected. Kbridge vs. pressure @Troom 3.5E-03 Kbridge, V/V, or Vbridge@Vexc=1V 3.0E-03 2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04 0.0E+00 0 10 20 30 40 50 60 70 80 90 100 -5.
The sensor output at room temperature and 100% of applied stimulus is emulated by this channel. The rotary switch S1 is used to select this channel. When the channel is selected, LED D108 will light to indicate that the correct channel is selected. Kbridge vs. pressure @Troom 3.5E-03 Kbridge, V/V, or Vbridge@Vexc=1V 3.0E-03 2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04 0.0E+00 0 10 20 30 40 50 60 70 80 90 100 -5.
The other channels are set in a similar manner and selected using S1.
Diode Vo: Generate Diode Voltages based on Operating Temperature Range The second tab in the spreadsheet allows the user to enter the temperature range and room temperature diode voltage (light blue areas). The spreadsheet calculates the diode voltages and displays the results in the yellow areas. Note that the Temp ADC area is specific to the PGA309 sensor signal conditioning chip. The Temp ADC values will be used in the computation of the Counts for the temp ADC.
The temperature output signal at cold temperature (-45°C) is emulated by this channel. The rotary switch S2 is used to select this channel. When the channel is selected, LED D201 will light to indicate that the correct channel is selected. NOTE: When emulating Diode temperature control, the Rt temperature section is not used.
The temperature output signal at room temperature (25°C) is emulated by this channel. The rotary switch S2 is used to select this channel. When the channel is selected, LED D202 will light to indicate that the correct channel is selected.
The temperature output signal at hot temperature (85°C) is emulated by this channel. The rotary switch S2 is used to select this channel. When the channel is selected, LED D203 will light to indicate that the correct channel is selected.
Generate Rt Voltages based on Operating Temperature Range and System Parameters The third tab in the spreadsheet allows the user to enter the temperature range and other system parameters in the light blue areas. The spreadsheet calculates the voltage level of the temperature signal and displays this in the yellow areas. Note that the Temp ADC area is specific to the PGA309 sensor signal conditioning chip. The Temp ADC values will be used in the computation of the Counts for the Temp ADC.
The temperature output signal at cold temperature (-45°C) is emulated by this channel. The rotary switch S2 is used to select this channel. When the channel is selected, LED D204 will light to indicate that the correct channel is selected.
The temperature output signal at room temperature (20°C) is emulated by this channel. The rotary switch S2 is used to select this channel. When the channel is selected, LED D204 will light to indicate that the correct channel is selected.
The temperature output signal at hot temperature (90°C) is emulated by this channel. The rotary switch S2 is used to select this channel. When the channel is selected, LED D204 will light to indicate that the correct channel is selected.
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Parts List, cont’d SBOA102A January 2005 Sensor-Emulator-EVM System Reference Guide 46
SBOA102A January 2005 Sensor-Emulator-EVM System Reference Guide 47
