Tooth Fairy Traditions...
The Melt Pressure Sensor is any device that converts this value into a signal output that can be observed by an operator or instrumentation, allowing a physical value to be measured. Pressure Sensors are used in a variety of applications to help operators monitor and control process stability while maintaining operator safety.
Our topic focuses on the melt pressure Sensor used in plastic extrusion and injection molding. The signal output from the sensor should be calibrated by instrumentation. This is vital for the accuracy and reliability of the pressure measurement.
To compensate for the effect of temperature at zero, the transducer must be in standby (no pressure applied) and appropriate calibration when at operating temperature.
All MPS pressure transducers contain a degree of temperature effect above zero, which can vary depending on the selected filler medium in the transducer capillary.
The physical properties of the liquid filling medium affect where the signal's zero output level will be, and this value needs to be taken into account when assigning the interval by instrumentation and adjustments are made to compensate.
This setting is similar to determining a Tare on a scale where the temperature effect is equivalent to the package of the product you are weighing.
The published temperature effect for 3 liquid filling options is as follows:
Hg = 15 psi / 100 ° F or 27 psi / 100 ° C
Fat = 36 psi / 100 ° F or 65psi / 100 ° C
NaK = 30 psi / 100 ° F or 54psi / 100 ° C
Based on these values, the process will need to be configured to accept the signal input as zero by calibrating the operating temperature.
Example: Process temperature = 400 ° F, Hg type sensor showing 60 psi signal output at zero pressure *
* Depending on the full scale pressure range of the transducer, this closed set will be in addition to our normal combined error specification, so the 10,000 psi range containing 0.5% combined error (+/- 50 psi) will look real anytime having 110psi or more offsets .
When calibrating, it is important to verify that no changes have been made to the signal output, only that the model specifications of the output are still within tolerance.
MPS devices 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 keystrokes.