Is it the PID or thermocouple that is broken?

[nutty_gnome]

So I have a dilemma – The short version is: how do I know if it is the PID or the RTD probe that is messed up?

So…. I have a ‘direct from China’ RTD probe that looks pretty nice. It is this one here: http://www.amazon.com/gp/product/B00FHVBKC4/?tag=skimlinks_replacement-20. It looks like a solid no-nonsense piece of equipment. It does not appear to be flawed or leaking, and electrical tests seem to work at room temp.

And I have this PID (a Fuji PYZ-5) which was a donation. Aside from it being old, I was told nothing about how it works. Here is the manual http://home.hit.no/~finnh/lab_fuji_controller/TN2PYZDe-E.pdf. It is an OLD PID. I know that.

Here is where it went wrong: I put the temp probe in a tee after my pump and plugged it into the PID. At this point, the whole system exists to ONLY read the temp of the fluid flowing in the tee past the pump. The PID reads a normal temp at room temp and, as I add heat and circulate water, the PID indicates that temperature is increasing. Then, at a random point after 125 deg F, the PID reverts to showing ‘UUUU’ in the display indicating one of the following conditions (from page 6 of the manual linked above)

Burnout of resistance bulb sensor (upscale burnout) -① In case of upscale burnout (standard) OFF or less than 4 mA in reverse action ON or more than 20 mA in normal action.

Or

PV reading is more than "the range upscale value +30% FS" NOTE: Even when the PV value is over the range within +30% FS, it becomes sensor burnout display, and the control output is output, if the input voltage exceeds the burnout detecting point.

I have run tests and found that the error occurs at seemingly random temps. Once at 125, once at 167, another time at 150F. I am going to try some more with boiling water tonight… but I want to know what I can do to see if it is the PID or the RTD that is causing this trouble? Any ideas or thoughts on tests to run?

I don’t mind buying a new PID or RTD if that is the problem… but I don’t want to buy a PID and a new RTD if only one of them is causing the trouble. Thanks in advance! N_G

 

[Indian_villager]

I have Fuji PID controllers. Have you set the parameter in the controller to let it know that it is working with a PT100 sensor?

Also the Fuji's allow you to set the upper and lower limits of the sensor. Check that whoever gave it to you didn't have it spanned to a different sensor.

 

[nutty_gnome]

It is set for PT100. I don't know about the upper and lower limits. Thats an interesting thought.... Can you help me understand where to look in the manual?

 

[Brumateur]

See the table 6-1 (P-SU) value. It's the same menu where you set up probe type (P-n2) parameter.

You can check your probe using multimeter. Jut read a probe resistance between the red and any of the blue terminals. It should gradually increases from around 110 Omh to around 140 Omh when you heat it from room temperature to a water boiling point.

 

[Indian_villager]

Set the P-SU value to 500 and see if that helps. It could also be something simple as a loose wire.

 

[nutty_gnome]

Thanks.... I 'll look into it. When you say loose, do you mean in the probe or in the PID? The probe is what it is... it isn't going to come apart easily. The PID... I have had that open in the past. There aren't all that many wires in there... just circuit boards and stuff. I'll look more closely tonight.

Is it normal for the probe to read 100 Ohms at room temp? I think it was reading that at about 60 deg in my basement last night. N_G

 

[Brumateur]

Pt100 resistance table:


Note cheap multimenters may have a few omh offset.

 

[nutty_gnome]

So I fixed the input maximum... It was set for 100F. I set it to 500F and the probe tracked temp properly from 60 deg to boiling water. We'll mostly properly. It seems to be reading low... I had water boiling at 204 deg F and two other thermos registering the temp as around 211F. I mucked around with the PV offset but the offset needed at 211F was more than required at 160..... So I don't know,... Guess I will still be checking things with other thermometers.

I kinda thought RTDs were supposed to not have these inaccuracy issues.


Sent from my iPad using Home Brew

 

[Indian_villager]

I'm glad we are getting you closer. Try setting that P-SU value to 750. Sometimes the voltages are spanned to the upper limit, so if you have the wrong upper limit set it will be a bit off.

 

[nutty_gnome]

I have been wondering if it wasn't the way I dangled the probe in the boiling water that depressed the temps. There is a significant chunk of 1/2 in MPT metal behind the 2 inch probe in non-boiling water that may be influencing temp at the junction. I will increase the P-SU value but also take more care to get the bulk of the probe heated.

The funny thing is that when it was all installed in the rig i found that prior to the PID reporting UUUU, the temps from the probe tracked with the temps in the pot. Maybe I just need to do a full scale run next time.

 

[rgauthier20420]

Your probe is going to have a different offset and boiling than it is going to have at mash temperatures. You should set the offset accurately to whichever one your going to be using it to measure.