The data of the differential resistance sensor is fluctuating greatly, with about 11 bits fluctuating.

天天1

The data of the differential resistance sensor is fluctuating greatly, with about 11 bits fluctuating. [Copy link]

The input voltage is 12V, which is converted to 5V by 7805, and then converted to 2 3.3V by LM117-3.3. The analog circuit and digital circuit are powered respectively. The 2.5V reference generates 2.5 voltage, and then the constant current circuit is designed by the op amp to measure the two resistors of the differential resistance sensor. I want to measure the resistance of different differential resistance sensors by switching the analog switch. At present, it is found that the voltage collected by the circuit jumps a lot, and only the first 13 numbers are stable. It is not difficult for a 24-bit ADC to achieve 16 to 18 bits of stability. Is this where my design needs to be improved? In addition, there are 2 analog switches. When one is connected to the sensor and the other is not connected to the sensor, the voltage can also be measured when measuring the data of the group without the sensor. The voltage size is similar to the data measured by the group with the sensor.

A five-wire differential resistance sensor is used, which actually has two resistors. Red is connected to the middle end of the two resistors, black and blue are the two wires printed on the same end of the sensor, and green and white are the two wires printed on the other end. Currently, the voltage jump between the black-red and green-red wires is large, with a jump of about 11 bits.

天天1

chunyang

First use an oscilloscope to observe whether it is caused by interference coupling.