Temperature control

kamau · Feb 19, 2009

hi guys,i urgently need you experience; i use a pt100 temp sensor in our tubular heat exchange steriliser,the product being sterilised is concentratd pineapple juice,the heated water temp is raised to 104 degrees,and in heat exchangig the product must attain a temp of 94 degrees this of coarse lowering the hot water temp.the result is that the temp trace on the recording chart have 3degrees variation hence a zigzag trace.our quality control dept.would like to have a trace close to a straight line.is it possible? am using 6-30psi 4-20ma i/p transducer and a commadder 1900 temp controller,the steam pressure is 109 psi.

Bitmore · Feb 19, 2009

If the temperature history trace is zigzaging there are some things to look at. If you are using a PID loop controller then reduce your PID proportional gain, then increase the integral gain. Remember to write the values down before changing them so if you run into problems you can go back to what was there before changes were made. There are allot of great discussion threads on this board about PID tuning.

Tom Jenkins · Feb 19, 2009

You might want to run a test with the control locked in manual and determine how much of the signal fluctuation is from the controller output and how much is just bounce in the signal. This will verify wether or not you need to look at noise in your temp sensors, actual fluctuation in temperature from steam variations, etc.

leitmotif · Feb 19, 2009

kamau said:
hi guys,i urgently need you experience; i use a pt100 temp sensor in our tubular heat exchange steriliser,the product being sterilised is concentratd pineapple juice,the heated water temp is raised to 104 degrees,and in heat exchangig the product must attain a temp of 94 degrees this of coarse lowering the hot water temp.the result is that the temp trace on the recording chart have 3degrees variation hence a zigzag trace.our quality control dept.would like to have a trace close to a straight line.is it possible? am using 6-30psi 4-20ma i/p transducer and a commadder 1900 temp controller,the steam pressure is 109 psi.

So what you are doing is using
350F (165C) steam to heat water to 104C (?)
passing water thru heat exchanger
to heat pineaple juice to 94C. ????

Where is the temp recorder sensing point in all this? Final product temperature?

Are you controlling the steam using a solenoid valve or one with proportional ie throttling capability?

What is your water (104C) temperature to heat exchanger fluctuations?

I doubt if you will eliminate all fluctuation but you may be able to reduce it to +/- 1C or less.

Dan Bentler

Gil47 · Feb 19, 2009

If you are seeing a saw tooth zig zag then possibly your valve that is doing the control is over sized, or you I/P converter or the feed back positioner which should be fitted, are not as good as they need to be.
Monitor the 4 to 20 mA and you will probably find its % variation is alot less than 3 % variation you are seeing in the temperature, 3 % variation on 4 to 20 mA would be close to 0.5 mA

Temperature control

kamau

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Bitmore

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Tom Jenkins

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leitmotif

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Gil47

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