logic temperature control
logic temperature control
(OP)
I am looking for a unit which can simulatnaeously measure 3 k-type thermocouples, average the two which are the closed together (and thus rejecting the one which is furthers off) and control a heater unit to bring the temperature to a certain setpoint.
We already have a control unit to control 1 k-type thermocouple so something which could only measure the 3 thermocouples, average the two and send this to the control unit will do to
We already have a control unit to control 1 k-type thermocouple so something which could only measure the 3 thermocouples, average the two and send this to the control unit will do to





RE: logic temperature control
Plesae read FAQ240-1032
WEB: <http://geocities.com/nbucska/>
RE: logic temperature control
If it is for a product then by all means it should be a small custom micro board that does exactly what you want and can then signal errors with indicators and can have alarm points, etc.
Do keep in mind that you can always parallel T/Cs and they automatically average their readings.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: logic temperature control
I once did exactly the task you describe with a Honeywell hybrid controller, the HC-900, with its function block logic. The controller was ideal because the purpose was multi-zone temp control using average of closest 2 of 3 TC's in a zone. The controller had the I/O and the process logic run the PID for a complete job.
Dan
RE: logic temperature control
RE: logic temperature control
RE: logic temperature control
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: logic temperature control
Am I going to learn something here?
This is my understanding of thermocouple theory.
With the excepion of some "Legacy" instruments, modern thermo couples generate a voltage. Modern instruments read this voltage without loading the circuit so as to avoid IR voltage losses in the extension wires.
When you connect two different voltages together you get a current flow. The resultant voltage will be higher than the lower voltage and lower than the higher voltage.
The resultant voltage will only be the average when the total resistance of each branch is equal. That will mean that all connections and the length and gage of the extension wires must be equal. Otherwise the average will be weighted in favor of the thermo couple with the lower resistance to the instrument.
Not to say that this method cannot be used, but it is well to be aware of the conditions, limitations and possible pitfalls.
Respectfully
RE: logic temperature control
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: logic temperature control
It is by the way for a lab experiment.
What material should I use for soldering them together?
Thanks!
RE: logic temperature control
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com