Question

How do you calibrate a sensor for static calibration?

Answer 1

Static calibration refers to the input-output relations obtained when only one input of the instrument is varied at a time, all other inputs being kept constant.

To each constant input, which is measured with another instrument, we associate the sensor output. The plot of these points is the sensor static characteristic for that specific input.

Steps for calibration:

1. Identify all the possible inputs of the instrument.

2. Decide which of the inputs will be significant in your application.

3. Determine the apparatus and methods to control (vary or maintain constant) all significant inputs over the desired range.

4. By varying one input and holding the other inputs constant, develop the sensor input-output relations.

Example: Calibration of the pressure gage sensor

The objective in this example is to determine the relationship between the desired input (pressure) and the output (scale reading).

The first step of the calibration process requires identifying the desired, interfering and modifying inputs of the pressure gage.

In the second step you must determine how, or in what conditions, you are going to use the sensor.

For example, what will be the surrounding temperature? If the temperature (which is an interfering input for this sensor) varies over a large range during the normal use of the sensor, maybe you will have to do the (desired-input / output) calibration for different value of the temperature.

Then you must ensure that, by choosing the appropriate experimental conditions, all the inputs of the pressure gage, except the fluid pressure, are kept constant.

The fluid pressure (true value) must be varied with another instrument, in increments, over some range, causing the measured value also to vary:

The average calibration curve is taken as a straight line of equation:

qo = mqi + b

m and b can be obtained with the least-squares criterion.