A sensor is any device that provides measurement of a physical value, by converting this value into a signal output that can be observed by an operator or instrumentation. Pressure Sensors are used in various applications, to help operators monitor and control process stability, while maintaining equipment safety.
Our topic focuses on the melt pressure transducer, that is used in plastic extrusion and injection molding. The signal output from the sensor should be calibrated with instrumentation. This is considered vital to the accuracy and reliability of the pressure measurement.
Proper calibration should be performed with the transducer at rest (no pressure applied) and at operating temperature, to compensate for temperature effect on zero.
All Dynisco pressure transducers include a rating of temperature effect on zero, and this rating can change depending on the selected fill media in the transducer capillary.
Physical properties of the liquid fill media, will effect where the zero output level of the signal will be, and this value needs to be considered when assigning the range with instrumentation, and adjustments would be made to compensate.
This adjustment would be similar to setting a TARE on a balance, where the temperature effect is equivalent of the package of the product you are weighing.
The published temperature effect for the 3 liquid fill options are as follows:
Based on these values we expect that the instrument will need to be configured to accept the signal input as zero, by performing calibration at the operating temperature of the process.
Example: Process temperature = 400°F, Hg type sensor showing signal output of 60 psi @ zero pressure*
*Depending on the full scale pressure range of the transducer, this off set would be in addition to our normal combined error specification, so a 10,000 psi range that has a .5% combined error (+/- 50 psi) would actual appear to have an offset of 110psi or more at any time.
It is important to remember, that when we are performing calibration, there are no changes being made to the signal output, only verification that output is still within tolerance, of the model specifications.
Dynisco instruments are designed to make calibration of pressure sensors an easy process. Our indicators and controllers can test the high and low limit of the signal output with a few key strokes.
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