Resin's plants instruments

[Adee]

One of our PET resin plant is in a shut down mode and some of its instruments such as pressure transducers, flowrate measuring devices and temperature sensors are giving reading that doesn't make a whole lot of sense. For example the flow rate for Ethylene glycol is showing to be 200 Kg/hr but its not even possible since the plant doesn't have any material left inside it at all. Similary, one flow rate is showing -300 Kg/hr. Similar problems are being faced some temperature and pressure sensors.

Heres my question for Electrical engineers (Since, I am not one) are those false reading common for instruments? or we need to pull them out and re-calibrate them? so the flow rates show No flow at all i.e., 0 kg/hr or is there something about these instrument that they are only designed to work when something is actually flowing through them or else they will show strange readings?

I apologize if my question looks stupid :p but some input from y'all would be awesome ^^

[Tom]

Since multiple intruments are affected, I would look for electrical grounding or ground loop problems. A poor ground or multiple grounds with different electrical potential can put voltages into the system which are in the range of sensor voltages or even stronger. You could probable measure the voltages coming from the instrument while mounted on the equipment and then uninstalled from the equipment to see how much influnce the ground is having. Additionally any electrician or electrical engineer can measure the difference in ground potential between the equipment and the control system. If grounding is found to be the source of the problem there are specific remedies such as a common earth ground. Establishing a good ground and proper grounding practices and sheilding can be a big project, but often it is the only solution for sensor reading problems and data communication issues.

Once good grounding and sheilding is verified, then i would pursue zeroing and calibration.