Temperature measuring
Posted: Tue May 24, 2016 9:40 pm
I have a test jig that measures the temperature of 4 individually heated assemblies. When the jig was built I used 4 PID controllers, with PT100 sensors, one for each assembly to be measured.
All was well but lately the system has become erratic. On start up the displays can show as much as a 4 degree C span and all the sensors are in the same ambient environment. A offset can be entered to get them all back in line but eventually the error repeats. Interchanging the sensors was inconclusive. I plan on substituting precision resistors for the sensors to determine if the controllers or sensors are drifting. If it is determind that it is the sensors, what is the opinion as to changing them to type K thermocouples. The controller can accoodate RTD devices or thermocouples, so it would be is a low cost fix.
We have used this same combination of components to replace bi-metal thermostats in several laboratory incubators, and have had great success. So far this problem has been a bit of an enigma!
I am waiting for delivery of a 4 channel data logging thermometer with NIST tracable calibration to help determine the problem, and to use it as a secondary calibration reference. It uses type K termoocouples so I wonder if these are more stable than the PT100's?
If it turns out to be unstable controllers, does anyone have suggestions for a replacement?
They are used for temperature measurement only, so no control function needed. They operate from 120VAC, and fit a 1/32 DIN panel cutout.
The components used are from http://www.auberins.com
Miniature TD sensor Model Pt100MN
PID controller Model SYL-1512A
The floor is open for comments!
Opinions
All was well but lately the system has become erratic. On start up the displays can show as much as a 4 degree C span and all the sensors are in the same ambient environment. A offset can be entered to get them all back in line but eventually the error repeats. Interchanging the sensors was inconclusive. I plan on substituting precision resistors for the sensors to determine if the controllers or sensors are drifting. If it is determind that it is the sensors, what is the opinion as to changing them to type K thermocouples. The controller can accoodate RTD devices or thermocouples, so it would be is a low cost fix.
We have used this same combination of components to replace bi-metal thermostats in several laboratory incubators, and have had great success. So far this problem has been a bit of an enigma!
I am waiting for delivery of a 4 channel data logging thermometer with NIST tracable calibration to help determine the problem, and to use it as a secondary calibration reference. It uses type K termoocouples so I wonder if these are more stable than the PT100's?
If it turns out to be unstable controllers, does anyone have suggestions for a replacement?
They are used for temperature measurement only, so no control function needed. They operate from 120VAC, and fit a 1/32 DIN panel cutout.
The components used are from http://www.auberins.com
Miniature TD sensor Model Pt100MN
PID controller Model SYL-1512A
The floor is open for comments!
Opinions