Calibrating a strain gauge/thermistor

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In summary, to calibrate a strain gauge or thermistor using a wheatstone bridge, you must use an arrangement of resistances supplied from a stable voltage source. The bridge must be balanced by adjusting the ratio of resistances in each branch. Any change in resistance from the sensor will produce a potential difference between two junctions, which can be used to calculate the amount of displacement. R4 is used to compensate for temperature variations, R3 balances the bridge, R2 is replaced by the transducer, and R1 ensures the ratio of resistances is balanced.
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Homework Statement



Hey guys,

Im abit confused on the method of calibrating a strain gauge/thermistor, i know they both use a wheatstone bridge (resistance). At the moment i have gathered this information,

Transducers and sensors which produce a change in resistance are typically used in a bridge circuit. This consists of an arrangement of resistances supplied from a stable voltage source. For the bridge to be balanced, the ratio of resistances in each branch must be balanced. Any change in resistance will produce a potential difference between the two junctions. The values of resistance are designed so that the small change in resistance from the sensor will result in an improvement in resolution of the measurement.

Equations i have gathered:

VA=R3/(R3+R1)*Vin

VB=R2/(R4+R2)*Vin

Once i have found the two node voltages am i to substract them from each other to find the difference between them?

and from that answer can i then say for example i got a voltage output of 1v, can i say that 1v is equal to 1m in displacement for the strain gauge?

ive read that R4 is used to compensate for temperature variations and it is not subjected to stress, R3 is used to balance the bridge, R2 is replaced from the transducer and i am not sure what R1 is used for?


Homework Equations



V_A=R3/(R3+R1)*Vin

V_B=R2/(R4+R2)*Vin

R2/R4=R1/R3


The Attempt at a Solution

 
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  • #2
Yes, once you have found the two node voltages you can subtract them to find the difference between them. This difference will give you a voltage output which will correspond to the amount of displacement in the strain gauge. R4 is used to compensate for temperature variations, meaning it is not subjected to stress and will remain constant. R3 is used to balance the bridge, while R2 is replaced by the transducer. R1 is used to make sure that the ratio of resistances in each branch is balanced. This is expressed as: R2/R4=R1/R3.
 

FAQ: Calibrating a strain gauge/thermistor

What is a strain gauge/thermistor?

A strain gauge is a device used to measure the strain or deformation of an object. It works by converting mechanical displacement into an electrical signal. A thermistor, on the other hand, is a type of temperature sensor that changes its resistance based on temperature.

Why is it important to calibrate a strain gauge/thermistor?

Calibration is important to ensure accurate and precise measurements. Over time, strain gauges and thermistors may drift or become less sensitive, which can affect the accuracy of their readings. Calibrating them helps to correct any errors and maintain their accuracy.

How do you calibrate a strain gauge/thermistor?

To calibrate a strain gauge, first, you need to apply a known force or weight to the object being measured. Then, measure the corresponding electrical signal from the strain gauge. By comparing the applied force to the measured signal, you can determine the sensitivity and make any necessary adjustments. For thermistors, you can use a calibration bath or standard reference thermometer to establish accurate temperature readings.

What factors can affect the calibration of a strain gauge/thermistor?

Several factors can affect the calibration of strain gauges and thermistors. These include temperature, humidity, aging, and environmental conditions. It's essential to consider and control these factors during calibration to ensure accurate and consistent measurements.

How often should a strain gauge/thermistor be calibrated?

The frequency of calibration depends on several factors, such as the application, the manufacturer's recommendations, and the level of accuracy required. In general, strain gauges and thermistors should be calibrated at least once a year. However, if they are used in critical applications, they may need to be calibrated more frequently, such as every six months.

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