# sensor excitation circuit

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#### hemnath

I have a pressure sensor excitation and signal conditioning circuit.

Attached is the circuit and recordings are posted below.

I have applied pressure of 20 bar and excited the current of 0.5mA to sensor.

Voltages are measured at output of sensor varies from 21.021mV to 21.030mV.

The op amp output voltage varies from 0.44097mV to 0.44130mV. Because of these changes in mV signal, my display value is fluctuated. (display and micro controller is not shown in the diagram)

Is it possible to stabilize the output voltage? Have to add any filtering?

#### Attachments

• Sheet1.pdf
38.5 KB · Views: 9

#### KlausST

##### Super Moderator
Staff member
Hi,

What is the referenc of the ADC?
For best overall performanc the excitation should use the same ref.
Imagine you use 3V3 as reference for both the sensor and the ADC. If volrage changes +5%, then sensor excitation voltage also changes 5%. Since sensor output depends directely on input voltage - it also changes 5%. After amplification there is still +5% at the ADC inputs. But ADC range also changes +5% means that the output code has no change... it is not involved by the 5%.
Mind: often VRef is low pass filtered - either use a single filter for both or use the same filtercharacteristic on both...

*****
* check if current regulation works. If you use a high ohmic ( more than 3k, depending on current regulator voltage drop) sensor, then the current regulation is useless.

* please add lowpass filter in your signal lines to improve signal to noise ratio. Maybe max pressure signal frequency is 10Hz, then select cutoff frequency so that mains frequency is attenuated.

* common mode voltage: if yor sensor is low ohmic, lets say 600 Ohms. Then excitation voltage is about 600 Ohms x 0.5mA = 300mV.
Common mode sensor output voltage then is about 150mV. Check if this is meets the common mode input voltage range of your opamps. Then you have a signal gain of 20. Check that no opamp output is saturated at negativ supply rail.

* lowering the opamp circuit resistors may also reduce noise.

Hope this helps

Klaus

#### mickjude

##### Newbie level 1
I have a pressure sensor excitation and signal conditioning circuit.

Attached is the circuit and recordings are posted below.

I have applied pressure of 20 bar and excited the current of 0.5mA to sensor.

Voltages are measured at output of sensor varies from 21.021mV to 21.030mV.

The op amp output voltage varies from 0.44097mV to 0.44130mV. Because of these changes in mV signal, my display value is fluctuated. (display and micro controller is not shown in the diagram)

Is it possible to stabilize the output voltage? Have to add any filtering?

Pls do you have a pir sensor circuit

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