Hi, I need to monitor the temperature control of a machine.
The machine uses J-type thermocouple sensors associated with a PLC (whose hex code is protected, not any data output other than an HMI LCD display).
My initial idea was to associate a J-type thermocouple reading module, in parallel with the present control system.
I wonder if this would theoretically work, and if other better ways to do this monitoring.
Obs: Put another temperature sensor and not feasible.
JoaoAnacleto:
Obs: Put another temperature sensor and not feasible.
What does this phrase mean?
Thermocouples generate tiny voltages. While you could attach one thermocouple to two measurement units, it is almost 100% certain they will interfere with each other.
You really must use a separate sensor. If your temperature range allows, choose a digital sensor such as a DS18B20.
The phrase means that it is an internal sensor in the machine, not more physical space to put another thermocouple sensor in that position, and presto monitor that specific position
Since the PLC is sealed, you would not even know if your unauthorized additions are interfering with it.
I think you are out of luck. Without access to the PLC and no space to put another sensor you simply cannot do it.
Use your own sensor to monitor the temperature at a position close and thermally connected to the sensor already in place.
The temperature gradient between the two positions can be found by experiment.
A thermocouple is basically a "source" of variable voltage. and the reading of this tension gives us a temperature.
If I read this voltage on the Arduino, and then used a voltage controller to play the same voltage at the inputs of my clp, would I be able to "replicate" that reading?
JoaoAnacleto:
Hi, I need to monitor the temperature control of a machine.
The machine uses J-type thermocouple sensors associated with a PLC (whose hex code is protected, not any data output other than an HMI LCD display).
My initial idea was to associate a J-type thermocouple reading module, in parallel with the present control system.
I wonder if this would theoretically work, and if other better ways to do this monitoring.
Obs: Put another temperature sensor and not feasible.
I suspect standard thermocouple amps are not designed to work in parallel on the same
thermocouple. However if the voltages are compatible in theory you just need a good instrumentation
amp across the thermocouple leads to boost the difference in voltage - the problems tend to be when
one unit is powered and the other isn't, or if one unit's ground is different, or supply the opposite polarity,
etc.
The first step is to measure the voltages at the thermocouple leads.
JoaoAnacleto:
A thermocouple is basically a "source" of variable voltage. and the reading of this tension gives us a temperature.
If I read this voltage on the Arduino, and then used a voltage controller to play the same voltage at the inputs of my clp, would I be able to "replicate" that reading?
Yes. But how will you test that the simulated input to the black box is correct?
MorganS:
Yes. But how will you test that the simulated input to the black box is correct?
Yes, this is a difficult problem, since you have to create a floating highly accurate dc voltage
of low impedance - would take some careful precision analog design as the voltages may be in
the order of fractions of a millivolt
My CLP has an HMI that shows the current reading value.
During a research on this subject, I found information that says the temperature and high impedance reader module.
Would pairing two high impedance readers in parallel generate such interference in reading?
Probably. You would have to test it extensively.