Interfacing Pressure Sensor to logic device input pin

1. A Inc. G Interfacing Pressure Sensor to logic device input pin This presentation is partially animated. Click within the blue frame to access the control panel. Only use the control panel (at the bottom of screen) to review what you have seen. When using your mouse, make sure you click only when it is within the blue frame that surrounds each slide.

2. Pre-presentation Self Assessment Activity Your comfort level with your responses to the following 2 design tasks assessment tool should indicate if the presentation that follows will increase you knowledge base on the topic outlined by the questions in this tool.

3. Pre-presentation Self Assessment Activity Your task is to design an interface circuit that connects a strain gauge based pressure sensor to a TTL AND device so that an action will occur if the pressure sensor and a temperature sensor are active at the same time. Assume the temperature sensor is an active low temperature sense high device however; (a) Make the pressure sensor behave like an active high PSH. Make the pressure sensor behave like an active low PSL. (b)

4. “non-inverting input” + output - “inverting input” Comparator application Limit Sensor interface Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts.

5. V - = + out = V R V V V V pull up pull up pull up pull up out out or = 0 Volts + V V V V V V strain total total total strain strain Comparator application Pressure Limit Sensor interface Strain gauge A strain gauge is a thin flexible membrane with a resistor embedded in the film. Note: As the pressure changes the strain gauge bends and gauge resistance changes. Vstrain equals the voltage drop across the strain gauge. Vpull up equals the voltage drop across the pull up resistor, R pull up. Vtotal equals the Vstrain plus V pull up. Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts.

6. V out V R pull up pull up V V strain total Comparator application Pressure Limit Sensor interface Strain gauge The signal from this terminal; Needs to be monitored to determine if the pressure has changed from steady state value. May trigger a process change when the pressure exceeds its allowed limit value. Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts.

7. +12 V Power terminal for device + V total V R V R out tune - pull up pull up Power terminal for device -12 V V V strain total Comparator application Pressure Limit Sensor interface Strain gauge If strain gauge resistance chances from steady state value, op amp output voltage will continue to increase (decrease) until; Gauge resistance returns to steady state value. Output signal reaches maximum possible value. Needs to be monitored to determine if the pressure has changed from steady state value. May trigger a process change when the pressure exceeds its allowed limit value. Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts.

8. V out V total R V R tune pull up pull up V V strain total Comparator application Pressure Limit Sensor interface Strain gauge is now +12 V 5 V clamped between 0 V and 5 V Power terminal for device + an input to a logic device - Power terminal for device -12 V Needs to be monitored to determine if the pressure has changed from steady state value. May trigger a process change when the pressure exceeds its allowed limit value. Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts.

9. action V total R V R tune pull up pull up TSH V V strain total Comparator application Pressure Limit Sensor interface Strain gauge Vout is now an active high high pressure limit sensor +12 V 5 V Power terminal for device + PSH - Power terminal for device Temperature sensor is from a different part of the process. -12 V When the pressure goes down the op amp output goes to 0 volts and action signal remains passive. When the pressure goes up the op amp output goes to 5 volts. If TSH is active, action signal become active. Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts.

10. PSL action V total R R V tune pull up pull up TSH V V strain total Comparator application Pressure Limit Sensor interface Strain gauge Vout is now an active low low pressure limit sensor +12 V 5 V Power terminal for device + - Power terminal for device Temperature sensor is from a different part of the process. -12 V When the pressure goes down the op amp output goes to 0 volts. If TSH is active, action signal become active. When the pressure goes up the op amp output goes to 5 volts and action signal remains passive. Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts.

11. action V total R R tune 5 V pull up +12 V TSH + PSH - V pull up -12 V V V strain total Post Presentation Self Assessment Activity Your task is to design an interface circuit that connects a strain gauge based pressure sensor to a TTL AND device so that an action will occur if the pressure sensor and a temperature sensor are active at the same time. Assume the temperature sensor is an active low temperature sense high device however; (a) Make the pressure sensor behave like an active high PSH.

12. PSL action V total R R tune 5 V pull up +12 V TSH + - V pull up -12 V V V total strain Post Presentation Self Assessment Activity Your task is to design an interface circuit that connects a strain gauge based pressure sensor to a TTL AND device so that an action will occur if the pressure sensor and a temperature sensor are active at the same time. Assume the temperature sensor is an active low temperature sense high device however; Make the pressure sensor behave like an active low PSL. (b)

13. End of Presentation A Inc. G