irondesk40
Member
have a issue that i can not figure out what to do to correct. we have hundreds of machines that have molds with J type thermocouples that then go to a stand alone temperature controller such as a Fuji. Management now wants to replace those and have the plc control the temperature. I have posted earlier and with some advice from folks on this site been able on a work bench to accomplish that. I can heat a aluminum mode to the desired temp and maintain it.
Now here is the problem, the thermocouple is in a pre made housing that screws into the mold. Everything was working perfect until i happened to place my hand on one of the molds and was watching the input from the thermocoupler into the plc into a scale with parameters instruction and i saw that value start to jump around. on the display it went from 85 degrees which i had heated it to and maintained it jump around from +- 20 to 30 degrees. i have changed the filter on the input card to 10 hz. As a test i then took the 110vac that is feeding the power to the plc and connected a jumper from the ground and touched the side of the mold. The temperature reading really jumped around to as high as 300 degrees, i removed the ground wire and it went back to normal. i got some information from Ron on this site about using a ungrounded thermocouple but with the way these are mounted into the mold they touch the sides of the mold and the molds are attached to framing of the machine which will be grounded.
I hate to ask so many questions but i have called ab tech support and my local ab rep's control expert and they do not have a answer.
Any suggestions, etc. would be very greatly appreciated.
THANKS
Now here is the problem, the thermocouple is in a pre made housing that screws into the mold. Everything was working perfect until i happened to place my hand on one of the molds and was watching the input from the thermocoupler into the plc into a scale with parameters instruction and i saw that value start to jump around. on the display it went from 85 degrees which i had heated it to and maintained it jump around from +- 20 to 30 degrees. i have changed the filter on the input card to 10 hz. As a test i then took the 110vac that is feeding the power to the plc and connected a jumper from the ground and touched the side of the mold. The temperature reading really jumped around to as high as 300 degrees, i removed the ground wire and it went back to normal. i got some information from Ron on this site about using a ungrounded thermocouple but with the way these are mounted into the mold they touch the sides of the mold and the molds are attached to framing of the machine which will be grounded.
I hate to ask so many questions but i have called ab tech support and my local ab rep's control expert and they do not have a answer.
Any suggestions, etc. would be very greatly appreciated.
THANKS