rex c100 - wrong reading and in reverse

Thread Starter

omri_alma

Joined Jan 6, 2020
7
hi,
i'm using a rex c100 pid controller. the temp reading is super weird:
though the temperature is about 25 degrees celsius, the reading is 700 or so. i'm using a K tc and i've changed the input type in the menu and non gave me a normal reading.
the second issue, is that it reads backwards. when the system get hotter, the temperature seems to go down.

any ideas what i'm doing wrong?

thank you
omri
 

Thread Starter

omri_alma

Joined Jan 6, 2020
7
thank you alec_t!
i was always fortunate to work for companies with great electronic engineers, i feel i neglected this world of knowledge...

i switched polarity but the behaviour is the same.

the rest of the system is so:
25A 600V SSR connects through a diode to a heater of 1300W. the heat won't turn on, no matter the temp i set.
i wired according to:
 

Reloadron

Joined Jan 15, 2015
4,868
This should be the user manual for your controller. I would start by comparing the full model number to the manual to be sure the controller you have is the controller you want. Thermocouple input should be terminals 8 and 9 Positive and Negative respectively. Typical Type K thermocouple color code is Yellow Positive and Red Negative. Additionally in the case of bare wire. You can easily test the polarity of a Type K thermocouples. The negative wire is MORE magnetic than the positive wire. Just put a magnet up to each wire. One will be more magnetic than the other. It will be very noticeable.

Next make sure your controller is properly setup for a Type K thermocouple input. That is all covered and described in the user manual. This includes your output configuration for connections 4 & 5. My best guess based on your post is an incorrect setup.

Ron
 
A short across the thermocouple inputs with a piece of wire should read room or the minimum temperature that the controller can read.

As Ron said: Red is negative.
 

Thread Starter

omri_alma

Joined Jan 6, 2020
7
Thank you both!

So, shorting the 9 and 10 with a wire does give me the right temperature.
Also, i can hear the SSR working when i play with the set temp.
I'll check the rest of the circuit.

The exact model is REX-c100fk02-m*an
Reverse action. So i guess it is the wrong controller.
 

Thread Starter

omri_alma

Joined Jan 6, 2020
7
thanks!
yes, you're right about the thermister. i'll have a proper k type in a few days.

still, it should have activated the circuit when the SSR switched. i'll re-do the wiring and update.
 

Reloadron

Joined Jan 15, 2015
4,868
Also, i can hear the SSR working when i play with the set temp.
I have never heard a SSR "click". Cheap Chinese knock off versions frequently use a relay but as long as it works I guess it should do as long as it handles the rated current load. Your SSR should be in series with your load.

Ron
 

Reloadron

Joined Jan 15, 2015
4,868
Your part number:
The exact model is REX-c100fk02-m*an
The Control Out if it's an M would be dry contact relay output. That would be across pins 4 & 5. If that is what you have then it won't drive and SSR control in line without adding an external power supply.

Ron
 

Thread Starter

omri_alma

Joined Jan 6, 2020
7
Your part number:

The Control Out if it's an M would be dry contact relay output. That would be across pins 4 & 5. If that is what you have then it won't drive and SSR control in line without adding an external power supply.

Ron
thank you ron.
my wiring is exactly like in the youtube video i attached. where should i add a power supply?
or, which model REX C100 should i buy to use it as in the video?

thanks!
 

Reloadron

Joined Jan 15, 2015
4,868
Your control out is a normally open dry contact relay out. These are pins 5 and 5 respectively. The controller can be setup for forward or reverse action as in the relay out is active above or below a setpoint. You want to drive a SSR which uses a control voltage between 3 and 32 volts DC. A very common SSR with a very common 3-32 volt control voltage. You want things to look like this:

Temp Controller SSR.png

Ron
 

Reloadron

Joined Jan 15, 2015
4,868
If it doesn't work wired as drawn in post #13 something is very wrong. You even mentioned earlier you could hear the relay in the controller clicking. Everything assumes the controller is setup correctly and is the correct model number for what you want to do?

Ron
 
getting it to work means nothing.

At the very least you can start with a shorted TC and an incandescent light as load. With the PB set as high as it will go. II think), Reset minimum and D minimum. You should get proportional control from 0 to the PB setting. PB is either PB in display units ot 1/PB. So if ambiant is 25 and the SP is 35 with PB=10 that's 100%. Sp=30, that 50% out. You wont find this info anywhere.

If it's a self-tuning controller, steps in temperature > than the PB are required.

If it's not self-tuning, then .... PB is 1/gain, so the higher the PB the better the temperature control and the highest instbility.

reset or integral time - It purpose is to make the set point and measured value agree at the control point. With proportional only control, the setpoint wont agree with the measured value.

Derivative time the "D" - helps to prevent overshoots.

I was pretty good at maually tuning a controller.
 
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