Unstable PLD612 + PT100 temperature reading (a new twist)

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tward
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Unstable PLD612 + PT100 temperature reading (a new twist)

Post by tward »

I've got a slightly different characterization of the temperature fluctuation problem discussed on the following threads:
viewtopic.php?f=5&t=390
viewtopic.php?f=5&t=385 --> viewtopic.php?f=5&t=387

I've experienced the problem described, namely the temperature reading fluctuates rapidly in about a 5F range. (My display is set to PT10.0, thus showing tenths. The fluctuation is about 5F, not 0.5F.) At first I would only have the problem when a (Norpro immersion coil) heater was plugged in and also in the water bath with the PT100 probe. (The problem exists even if no power is flowing to the heater. Indeed the problem exists even when a) the alarms were set > the water's PV and b) SV < the water's PV - thus no alarms and no relay contact. For example, room temperature water with alarms at 250F and SV at 10F.)

OK, now here's the 'twist'. I unplugged the heater and removed it from the water, so it was no longer in play. I just held the probe near the neck of the probe and suspended it in the water, which was in a ceramic pot. If I hold it was bare hands while in bare feet on the tile floor the temperature fluctuates in the apprx. 5F range. If I either wear a rubber glove or rubber soled shoes, the fluctuations return to "normal" (less than 1F).

So all of this seems related to some sort of ground current / leakage.

Unfortunately, the jumper solution described in the above threads makes the temperature reading several degrees higher in room temperature water and made it read around 240F in boiling water. So I fear that in solving the fluctuation problem the jumper solution creates and accuracy problem.

Any ideas?
richiem
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by richiem »

I would first try connecting the shield only to terminal 10 on the 612.
I would make sure that AC hot and neutral aren't reversed somewhere -- like at the wall outlet, which is more common than you might think, especially in older houses.
You could try isolating the probe from the water with a tight-fitting rubber sheath, like a condom...
Tech_Marco
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by Tech_Marco »

Rich is correct. The shield must be connected to #10 but not #9. Just confirmed that with the manufacturer. Or, add a capcitor 1uF across #8 & #9, and #8 & #10. That should eliminate the noise problem. But I think it should be 100pF Give a try on both as it doesn't cost much for the small capacitor

Marco
richiem
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by richiem »

Marco, 100 picofarads is far too small to work as a filter in this low-impedance circuit. Two 1 microfarad capacitors, one connected from 8 to 9 and one from 9 to 10 will likely help a lot. They can be low-voltage caps rated at say 50V, but they should be mylar or polyester film caps, not electrolytics or tantalums.
Tech_Marco
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by Tech_Marco »

Thanks Rich. I was thinking that the capacitor was connecting to the ground to bypass noise. In fact, per manufacturer the controller doesn't has any 'Ground'. So 1uF or large cap is need for noise filtration. I will stock up the 1uF and/or 10uF for folks who may has noise issue, just in case they couldn't get it.

Marco
tward
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by tward »

Thanks richiem and Tech_Marco.

[I should note that I have the FILe (filter) = 0 in these tests.]

I switched the wires to #1 & #2 and that did not change the behavior.

I then took about a 1 1/2" piece of stranded, insulated #18 copper wire, stripped both ends and put an aligator clip on one end. I'll refer to that as the "jumper". I inserted the bare end of the jumper into the #10 spot where the PT100 'yellow' wire is.

When I completed the jumper by clipping it to the PT100 shield the temperature no longer fluctuates rapidly in an apprx. 5F range when I hold the probe with a bare hand while in bare feet on the tile floor. I tested in both room temperature air and room temperature / top water, both of which were roughly 67F. Inserting the plugged-in heater into the water bath also no longer caused an apprx. 5F fluctuation.

However, when I attach the jumper (clip the aligator clip onto the shield) the temperature reading spikes up about 8-10F and then settles down towards the reading that existed before the jumper was attached. (This happens consistently in air and water and regardless of whether I handle with a rubber glove.) Interestingly, the "settling" towards the original (non-jumpered) temperature reading appears like exponential decay. After the initial 8-10F spike the difference is cut down to about 4F within a few seconds and 2-3F in about a minute or so and seems to settle to a final reading 1.5 - 2.0F above the original after 5-15 minutes. So there remains an offset in the temperature.

I then built and ice bath and did some testing. With the jumper the temperature was 34.2 - 34.3. Without the jumper it was 32.4 - 32.6. So, again, we've got an offset in the 1.5 - 2.0F range.

I'm concerned that this offset may not be stable and thus could prevent a stable calibration.

Also of note is the behavior in ice water when the jumper is not attached and I hold the probe with bare hands with bare feet on the tile floor. The reading fluctuations are not in the 5F range; instead the fluctuation is in the 0.5F range, so the range of fluctuation shrinks to 10% of the value experienced at room temperature.

I then let it come up to room temperature and boiled water in this medium sized metal pot. Without the jumper the reading came up to 210-211F with fluctuations about 2F. If I touched the probe/shield with bare hands and bare feet on the tile floor I got the 5F fluctuations. When I attached the jumper the reading spiked to about 450F and quickly settled to about 300F and kept going down. Even after a few minutes it is fluctuating about 15F around 250F and after 20-25 minutes it was in the 230Fs with fluctuations around 5F. (Note that the metal pot was on a gas stove (metal).)

So... the jumper seems to help keep the temperature reading stable when the probe is exposed to some sort of 'ground loop' or something like that. But the jumper solutions also results in a temperature offset and this offset may be proportional instead of fixed (absolute).

So I still feel kind of stuck.

Would the capacitor solution solve the problem without the "side effect"?
richiem
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by richiem »

I think the circuits in the 612 do take a long time to settle when you make the changes you're making. Offset and linearity errors are fairly common in temperature detectors, though the Pt100 probes tend to be pretty good.

I think you're taking a risk by holding the gear in bare hands while barefoot on a tile floor -- not good safety practice. Be sure everything is plugged into a GFCI circuit on the AC line...

Terminals 1 & 2 have no polarity -- these are the AC power inputs and they don't care which polarity of the waveform comes first. Changing those wires will have no effect.

The capacitors are very likely the best solution, but it is possible that there is something wrong in the 612 itself that is causing these erratic responses. If the caps don't work -- and they are a real good idea -- then ask Marco for a replacement 612.
tward
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by tward »

richiem wrote:I think the circuits in the 612 do take a long time to settle when you make the changes you're making. Offset and linearity errors are fairly common in temperature detectors, though the Pt100 probes tend to be pretty good.

I think you're taking a risk by holding the gear in bare hands while barefoot on a tile floor -- not good safety practice. Be sure everything is plugged into a GFCI circuit on the AC line...

Terminals 1 & 2 have no polarity -- these are the AC power inputs and they don't care which polarity of the waveform comes first. Changing those wires will have no effect.

The capacitors are very likely the best solution, but it is possible that there is something wrong in the 612 itself that is causing these erratic responses. If the caps don't work -- and they are a real good idea -- then ask Marco for a replacement 612.
Thanks richiem. I'm going to figure out where to get capacitors that will easily make those jumps. The device is always plugged into a GFCI (which I do a push button test on before using).
tward
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by tward »

richiem wrote:Marco, 100 picofarads is far too small to work as a filter in this low-impedance circuit. Two 1 microfarad capacitors, one connected from 8 to 9 and one from 9 to 10 will likely help a lot. They can be low-voltage caps rated at say 50V, but they should be mylar or polyester film caps, not electrolytics or tantalums.
You'd mentioned 50V and I have not been able to find a mylar/polyester capacitor that's both 1 microfarad AND 50V. I did find one: NTE MLR105K250 CAPACITOR MYLAR POLYESTER FILM 250V 1.0MF. So it's rated for 250V. Would that work?
richiem
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by richiem »

Sure, but they're pretty large physically -- I actually think that 0.47uF units will work fine too. Check on eBay for 50V, 63V, or 100V units -- they'll be easier to handle. If you get desperate, send me a private message and I'll see what I can do.
tward
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by tward »

richiem wrote:Sure, but they're pretty large physically -- I actually think that 0.47uF units will work fine too. Check on eBay for 50V, 63V, or 100V units -- they'll be easier to handle. If you get desperate, send me a private message and I'll see what I can do.
Despite the excellent assistance I've found here, I find myself on the brink of a project fail. I've tried placing a mylar/film 0.47uF 100V capacitor (*) from 8-9 and another from 9-10. It seemed to help for a while and then it didn't. A first attempt with the probe and plugged-in heater in a room temperature water bath was encouraging - little fluctuation. Then the same thing in an ice bath. Then in boiling water even without the heater the temperature fluctuated between 210.2 - 211.9. This fluctuation seemed sinusoidal (rapid rise, then a crest, then a rapid fall, then a bottoming, then a rapid rise, etc.) (**). I then inserted the plugged-in heater into the water and the fluctuations increased. Later I tried the ice bath again, but this time when I inserted the plugged-in heater I experienced ~5F rapid fluctuations. I then tried room temperature water and the introduction of the plugged-in heater caused fluctuations even greater than 5F. Perhaps the capacitors are only initially effective while they store charge but once they store maximum charge they lose effectiveness?

I could try using a couple of multilayer ceramic 1uF 50V capacitors instead, but this is looking like a dead end at this point.

So... is there any way to figure out if this is the "fault" of my PT100 probe or of my JLD612 controller?



* Note:
I used two NTC model MLR474K100 capacitors. They are specified in the downloadable MLR Series pdf found at http://www.nteinc.com/capacitor_web/. The specs for this capacitor are:
The MLR series is a range of radial lead non-polarized polyester film (Mylar) capacitors dipped in a hard epoxy coating material to provide excellent protection against moisture.

Dissipation Factor: 1% Max
Capacitance Tolerance (K): ±10% measured @ +25°C (+77°F), 1kHz, for values up to and including 1μf
Insulation Resistance: 50V & 100V, .12μf - 2.2 μf = 10,000M[Omega] Min

100 Volt (65VAC) Series Dimensions (mm)
Cap μf Code T H L S d
.47 474 6.0 12.0 18.0 15.0 ±1.5 0.6


** Note:
The boiling water test was done in a stainless steel pot on top of a gas (metal) stove.
richiem
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by richiem »

The caps are fine, just right. Try connecting one cap from 8 to 9 and one from 8 to 10 -- to me, this is the preferred connection. And it may help to then add a third cap from 9 to 10... Sometimes these problems are a little pesky.

But I admit I'm mystified by these reports of noise pickup with Pt100 probes. They are low impedance, less than 200 ohms for most uses, which helps reduce noise per se; they're just resistors that happen to have a very stable and predictable change in resistance to a change in temperature; and they're quite durable. That said, your problem could be in either the probe or in the 612, and to confirm which, you at least need another probe.

I've seen them for very low cost, around $3, on eBay; I haven't looked to see what lightobject charges for them; in any case it wouldn't hurt to a spare. If you change the probe and have the same result, then the 612 may be the problem.

Hang in there, you're actually making progress; we always learn more when things don't work as expected.
tward
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by tward »

richiem wrote:The caps are fine, just right. Try connecting one cap from 8 to 9 and one from 8 to 10 -- to me, this is the preferred connection. And it may help to then add a third cap from 9 to 10... Sometimes these problems are a little pesky.

But I admit I'm mystified by these reports of noise pickup with Pt100 probes. They are low impedance, less than 200 ohms for most uses...
I don't have a third capacitor available to try the 8-9, 9-10, 8-10 configuration. However, I did try another PT100 - the identical model that I had (from Virtual Village) - and it seems the problem has gone away. So it seems that the problem was with the PT100. I'm not sure what type of flaw in a PT100 could have caused this problem...
Tech_Marco
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by Tech_Marco »

I think the issue is "isolation" issue. We used to sell PT-100 with shield grounded (non-isolated). But per customer request, we asked the supplier to make isolated PT-100 (cost a little more). Do me a favour, use a small wire to ground the pt-100 shield to one of pin: #8,#9,#100, one by one, see if it fix the problem. Also, please double check the connectors. Once I got this things staight out, I'll talk to the manufacturer to make changes

Thanks
Marco
tward
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Re: Unstable PLD612 + PT100 temperature reading (a new twist

Post by tward »

Tech_Marco wrote:I think the issue is "isolation" issue. We used to sell PT-100 with shield grounded (non-isolated). But per customer request, we asked the supplier to make isolated PT-100 (cost a little more). Do me a favour, use a small wire to ground the pt-100 shield to one of pin: #8,#9,#100, one by one, see if it fix the problem. Also, please double check the connectors. Once I got this things staight out, I'll talk to the manufacturer to make changes

Thanks
Marco
Note that I am not using a PT100 from Light Object. My PT100 was purchased from Virtual Village. I did try 'grounding' the shield using a jumper. I know I tried pin #9 and pin #10. I can't remember if I'd tried pin #8. Anyway, note that I replaced the PT100 with the identical make and model (the same PT100 from Virtual Village) and the problem appears to be solved. Thus, it appears that the problem was due to some fault in the manufacture of the specific PT100 probe I was using.
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