Bench Test Rig for TekMar 251

AlwaysLearning2024

Hi everyone,

Sharing a little project I set up to better understand the older TekMar 251boiler control.

I simulated the following using resistor values:

• 32F outside temp (using 30K resistor)
• 140F Supply Pipe (using 3.3K resistor)
• Variable room temp simulation using a resistor substitution box.

This is teaching me how the device responds with different sensor settings.

EdTheHeaterMan

Fascinating

109A_5

Since a real live operating system is more dynamic than fixed resistors, I probably would have used 10 turn potentiometers instead of fixed resistors. Depending on what you want to learn you could automate the process.

One variable resistor example.

US Stock 2 Sets 100K Ohm 3590S Potentiometer 10 Turn Counting Dial Rotary Knob

https://www.ebay.com/itm/401564815576

AlwaysLearning2024

Thank you @109A_5 ! Great idea!

hot_rod

tekmar has a simulator available, a bit pricey

I got a plastic project box, 10 turn POTS and little rebel resistors to make a simulator for the Resol controls. Under 100 bucks

109A_5

Yes if you know the sensor (thermistor) resistance range you want, you can refine the variable resistors used and use fixed resistors to more closely define the variable range.

The numbers on the scales on the simulator seem odd.

109A_5

109A_5

OK I think they are fixed values of resistances representing specific temperatures and not variable like a potentiometer. A thermistor would be variable. I guess whatever works best for whatever you are trying to achieve.

mattmia2

there usually is a chart for the thermistor values in the manual. you could use a pot and fixed resistor in series to simulate normal temps. looking at those temp values you might need a log taper pot.

109A_5

I doubt a log taper or audio taper pot would match the curve of a thermistor, I would think using the "Counting Dial Rotary Knob" it would be easier to track the resistance of a 100K Pot, 10K per turn and the knob has 100 count indexing.

hot_rod

The Resols use a 10k thermistor turning the pot simulated a changing temperature conditions to set, change and confirm operating conditions

We used it for over the phone tech support calls to walk a customer through settings or a troubleshoot.

My son worked for a tekmar rep and they used the simulators for classroom training sessions