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Are you sure they are RS-232 and not RS-485/422? Here some -vague- thoughts because we need more information regarding the protocol to use and final check of that the physical interface type. RS232/422/485. Sometimes you can configure the ports as being Modbus-RTU ports. With an USB to RS485...

Also remember: Power (watt) is linear. Voltage and current is not!

The units are indeed very important. It depends on the brand of controller you use if the P setting is in either % of the measurement range or in °C. The I and D settings are (most of the time) in seconds and (not so often) in minutes. Tuning such a cascaded loop is indeed trickier. When I...

Is your P setting in % of the range of in °C? In both cases 4 is quite low to start with. I would try to start with a larger value of i.e. 25% of your measurement range or 25°C. So your process does not behave in an on/off way. An I value of just 4 seconds is also very low. See what happens when...

Yes I also thought that way when I came from the school. A normal behaving temperature process, like for example an oven, doesn't have a D-action. Also controlled many ovens with just PI controllers without D action because in the model the process of most ovens just behave like an integrator...

Ok that is really nice that you can calculate the response this way, and also so very fast. But coming from a practical point of view, which P, I and D settings you arrived at? I understand this is for 1 PID controller and not a cascaded system?

pnachtwey said: "One must be able to write differential equations that express the non-linearities etc. I write my own system identification, model generation and gain calculation software. I doubt you can find an off the shelf package that can handle more than the standard cases. Differential...

Theoretically everything can be calculated. But in a practical situation the model is always lacking something and there can be non-linearities in the process and dead-times. Then the modelling takes much more time than just a few hours of tuning. Sometimes you just need to be pragmatic and...

Some info on tuning. It is very important to use a registration system that registrates the measured temperature as well als the temperature setpoint. This way you can see if oscillations of the measured temperature get bigger or smaller incl. frequency changes. You can use a computerized...

Dear Farahgan, Am I understanding this correctly? Your are using a modicon PLC of this type...

An I time of just 4 seconds (am I understanding it correctly) is quite low for a large system like this Is the P setting 4°C or 4% of the measurement scale? Both also pretty low. With too low settings you get oscillations. Experiment with larger settings and see what happens. Technically...

Dear David, Ok, nice to hear that your apprentices started with the test-system. Looking forward to results and even more: pictures! gr. Patrick

Are you 100% sure that the settings for the communication are set correctly? Sometimes the default is not the best. In various systems you can set for example a "wait to send" parameter. This means that the system waits a short while in order to let the signals become stable (after switching...

Dear David, We work a lot with various thermocouples of various types. Always remember that you have to use the cable and connectors for that specific thermocouple type if you want to measure correctly. Otherwise you will have a temperature deviation. But if it is not such a big problem you can...

Copper works ok for RTD, it makes sense however, to use at least 3, or better 4 wire RTDs to compensate for the resistance in the cable. If you want to be 100% sure and you must use a 2 wire RTD: make sure the cables have least resistance possible (so use thick cables) to prevent extra...

When using electromechanical relays that have to switch power, our experience is that you must not use a shorter control cycle time of 10s. So, when the controller output wants 50% power, you switch the relay on for 5 sec and off for 5 sec. When the controller wants 80% you switch it on for 2...

No problem with a Pro-face touchpanel. Writing data to CSV files is standard functionality in the development tool software. You can write the measured value (or a calculated value) to a standard CSV file on SD-card or USB stick. It is also accessable remotely with FTP.

Follow the advice of Mr. Schulze closely. Normally speaking 32 is the max. limit for driving the bus, so I would make a 2nd trunk or split the 33 modules in 16 and 17 slaves on 2 buses... Your bus driving electronics must also be able to drive the signals on the bus, that is what is normally...

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Dear Satish, Of course you can. It would help if you would specify frequency+power in watts and modulation type. But if you keep the polarization vertical you can use an omnidirectional vertical antenna in the center and use yagi directional antenna's around it. You also have to use them...