Interfacing Pressure Sensor to logic device input pin 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. This presentation is partially animated. When using your mouse, make sure you click only when it is within the blue frame that surrounds each slide. A G Inc.

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. 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. (b) Make the pressure sensor behave like an active low PSL.

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

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

Pressure Limit Sensor interface Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts. Comparator application Strain gauge V strain V total R pull up V 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. V out

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

Pressure Limit Sensor interface Operational Amplifier’s only Rule of Operation If the two inputs signals are equal, then the output signal is zero volts. Comparator application +12 V -12 V Power terminal for device Strain gauge V strain V total R pull up 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. V total R tune 5 V clamped between 0 V and 5 V V out is now an input to a logic device

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

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

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 V -12 V V strain V total R pull up V + - V total R tune 5 V TSH action PSH

(b) Make the pressure sensor behave like an active low PSL. 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; +12 V -12 V V strain V total R pull up V + - V total R tune 5 V TSH action PSL

End of Presentation A G Inc.