Summary of Instrumentation Amplifier For Pressure Sensor
This project describes a general-purpose differential amplifier board for piezoresistive pressure sensors. It amplifies low differential outputs (25–50 mV) to a single-ended voltage suitable for microcontroller ADCs (0.75–4.75 V), uses an LM358 dual op amp in an instrumentation-amplifier configuration, includes trimmer potentiometers for offset (PR2) and gain (PR1), supports dual sensor footprints (MPXM2010GS and MPXV2010DP), and offers dual-supply or single-supply operation with a 0Ω option in place of C8.
Parts used in the General purpose differential amplifier project:
- LM358 dual operational amplifier
- Multiple resistors (fixed resistors as per schematic)
- Trimmer potentiometer PR1 (gain adjustment)
- Trimmer potentiometer PR2 (offset adjustment)
- Capacitors (including C8)
- 0Ω resistor (option in place of C8 for single supply)
- MPXM2010GS sensor footprint
- MPXV2010DP sensor footprint
- Dual sensor mounting/options
- 4-pin header connector for external sensors
- PCB with instrumentation amplifier layout (example from NXP AN1318 Figure 2)
General purpose differential amplifier project has been designed for various pressure sensor amplifier applications. Circuit provided with multiple resistors, capacitors, dual sensor options and 4 pin Header connector to interface other external sensors. Schematic is an example from NXP application AN1318 Figure 2.
The most popular silicon pressure sensors are piezo-resistive bridges that produce a differential output.
Voltage output is in response to pressure applied to a thin silicon diaphragm. Output voltage for these sensors is generally 25 to 50 mV full scales. Interface to microcomputers, therefore, generally involves gaining up the relatively small output voltage, performing a differential to single ended conversion, and scaling the analog signal into a range appropriate for analog to digital conversion. The circuit published here is simple solution which amplify low voltage differential signal and provide single output voltage which can be directly feed to ADC of micro-controller. Instrumentation amplifiers are by far the most common interface circuits that are used with pressure sensors. An example of an inexpensive instrumentation amplifier based interface circuit uses an LM358 dual operational amplifier and several resistors that are configured as a classic instrumentation amplifier with one important exception. PR2 Trimmer potentiometer provided to set the offset voltage 0.75V. Setting the offset voltage to 0.75 V results in a 0.75 V to 4.75 V output that is directly compatible with microprocessor A/D inputs. Over a zero to 50° C temperature range, combined accuracy for an MPX2000 series sensor and this interface is on the order of ± 10%. Trimmer potentiometer PR1 helps to set the gain. PCB provided with MPXM2010GS and MPXV2010DP dual footprint options, for testing purpose MPXV2010DP sensors has been used.
The MPXV2010 series silicon Piezo-Resistive pressure sensors provide a very accurate and linear voltage output directly proportional to the applied pressure. These sensors house a single monolithic silicon die with the strain gauge and thin film resistor network integrated. The sensor is laser trimmed for precise span, offset calibration and temperature compensation.
Note : Board is designed for multiple applications and has dual supply input option, Use 0E resistor instead of C8 or short the two terminals since circuit works on single supply.
Read more: Instrumentation Amplifier For Pressure Sensor
- What is the purpose of this differential amplifier project?
To amplify low-level differential outputs from piezoresistive pressure sensors and convert them to a single-ended voltage suitable for microcontroller ADC inputs. - Which op amp is used in the circuit?
The circuit uses an LM358 dual operational amplifier. - How are offset and gain adjusted?
Offset is set using trimmer potentiometer PR2 and gain is set using trimmer potentiometer PR1. - What output voltage range is provided for ADC compatibility?
Setting the offset to 0.75 V results in an output range of 0.75 V to 4.75 V compatible with microprocessor A/D inputs. - Which pressure sensors footprints are provided on the PCB?
The PCB includes dual footprints for MPXM2010GS and MPXV2010DP sensors. - What is the typical differential output of the pressure sensors this circuit targets?
The sensors typically produce a differential output of about 25 to 50 mV full scale. - Can the board operate from a single supply?
Yes; the board supports dual supply input option and can operate on single supply by using a 0Ω resistor instead of C8 or shorting the two terminals. - What accuracy can be expected over 0 to 50°C with an MPX2000 series sensor?
Combined accuracy for an MPX2000 series sensor and this interface is on the order of ±10% over 0 to 50°C.
