Panel mounts for RTD sensors

[KyleWolf]

so I am wanting a way to disconnect my RTD sensor from my control panel for ease of use, storage, cleaning, etc.

So, I figured instead of wiring my RTD sensor directly into my PID, how about I add a disconnect at the panel. I have seen this guy here at Auber Instruments, but I was just curious if any 3-pin plug would be sufficient. For example this 3-pin XLR audio connector and this XLR panel mount.

I can't imagine they are must different, but I just wanted to ask.

Thanks

 

[BrunDog]

Keep in mind that RTDs (Pt100's anyway) are low impedance devices, meaning they are low resistance and have a narrow band of resistance changes associated to temperature variations. This is great to reduce electric noise but any extra or aberrant impedance will affect accuracy. Resistance added may be the same across the signal and reference lines, but extra connections raise the probability of a difference. If you use a panel amount connector, make sure they are of good quality (e.g. gold contacts) and properly soldered (do not crimp).

I am sure someone will reply with the usual "I've never had a problem and/or my temps are accurate". This is probably true, but you can punch some holes in an airplane wing and the plane will probably fly, but at some point the holes are enough to cause it to crash. Dramatic, I know!

 

[augiedoggy]

so I am wanting a way to disconnect my RTD sensor from my control panel for ease of use, storage, cleaning, etc.

So, I figured instead of wiring my RTD sensor directly into my PID, how about I add a disconnect at the panel. I have seen this guy here at Auber Instruments, but I was just curious if any 3-pin plug would be sufficient. For example this 3-pin XLR audio connector and this XLR panel mount.

I can't imagine they are must different, but I just wanted to ask.

Thanks

I'll be that guy here Brundog,

I use the cheap 3 pin "aviation connectors" from ebay like these 99 cent ones here .. http://www.ebay.com/itm/GX12-Aviati...hash=item2835a911aa:m:mdd611i4zxiE-tZwWM199bQ ... after using about 40 or so now in all my panels and devices, I did have one that was touchy I had to replace but 1 out of 40 isnt bad since I saved quite a bit over aubers prices on these. (BTW the commercial flat bed printers I service use these exact same connectors and they start out at $75k for the printers and Ive never had an issue there from them either.)

I solder my wires on and will add I have never had strange readings or behavior from these other than the time or two I miswired them and learned fast they were as such..

I also use the slightly lager 16mm versions of these for my dc pumps. I have been using them for about 5 years now too.

BTW I do have about 7 or so of the same generic chinese connectors auberins sells with thier rtds(as well as ebay and aliexpress like offered here with an RTD http://www.ebay.com/itm/RTD-PT100-T...404095?hash=item2a849b69bf:g:hREAAOSwi8VZOkTx ) and they work well too but I actually prefer the aviation style since they are keyed better they are easier to plug in without fiddling to get them lined up.

I have yet to see anyone offering premade or even kits for sytems that use gold plated pins on these Brundog... I understand the theory behind them having an advantage but I just dont think its translates to a real world difference that can be appreciated here. Just my opinion though...

 

[BrunDog]

I hear you. And I agree it's probably not an issue most of the time. But these may not be high quality connectors. Just keep in mind RTD curves represent about 5 degrees F per ohm of resistance. That's a half a degree for a tenth of an ohm. So it would be very easy for some small resistance difference to build between pins, relegating your highly accurate Pt100 probe to be quickly off by a few degrees without you knowing about it.

 

[milldoggy]

so I am wanting a way to disconnect my RTD sensor from my control panel for ease of use, storage, cleaning, etc.

So, I figured instead of wiring my RTD sensor directly into my PID, how about I add a disconnect at the panel. I have seen this guy here at Auber Instruments, but I was just curious if any 3-pin plug would be sufficient. For example this 3-pin XLR audio connector and this XLR panel mount.

I can't imagine they are must different, but I just wanted to ask.

Thanks

Xlr work great

 

[Ozarks Mountain Brewery]

what BrunDog is trying to say is don't be surprised that after adding a quick disconnect you will need to recalibrate the pid, its normal, Ive done it many times and like above these are not the easiest to plug in when your in a hurry

 

[Smellyglove]

XLRs like mentioned above work great, but you need to recalibrate whenever you add a new piece into the RTD-line. Also it's nice (if you haven't already) with RTDs with detachable cables, so you can detatch them in both ends.

 

[BrunDog]

Yes, recalibration should be done... but not just once IMO. Probably every now and again if you are trying to get to an exact temp.

 

[KyleWolf]

Cool. Thanks everyone. recalibrating won't be an issue because when I put all of this together is going to be the first time the PID is calibrated.

 

[passedpawn]

Keep in mind that RTDs (Pt100's anyway) are low impedance devices, meaning they are low resistance and have a narrow band of resistance changes associated to temperature variations. This is great to reduce electric noise but any extra or aberrant impedance will affect accuracy. Resistance added may be the same across the signal and reference lines, but extra connections raise the probability of a difference. If you use a panel amount connector, make sure they are of good quality (e.g. gold contacts) and properly soldered (do not crimp).

I am sure someone will reply with the usual "I've never had a problem and/or my temps are accurate". This is probably true, but you can punch some holes in an airplane wing and the plane will probably fly, but at some point the holes are enough to cause it to crash. Dramatic, I know!

With a 3 or 4-wire sensor, not a problem.

This is the exact reason for 3 and 4-wire resistive temperature devices (thermistors, RTDs). Errors caused by IR losses in the wires are removed by measuring on the additional non-current-carrying wires. Because those wires aren't carrying any current, no ΔV drop. This assumes that the stimulation current through the RTD is created from a regulated current sink/source.

 

[BrunDog]

With a 3 or 4-wire sensor, not a problem.

This is the exact reason for 3 and 4-wire resistive temperature devices (thermistors, RTDs). Errors caused by IR losses in the wires are removed by measuring on the additional non-current-carrying wires. Because those wires aren't carrying any current, no ΔV drop. This assumes that the stimulation current through the RTD is created from a regulated current sink/source.

Well, that's not entirely accurate. What if the sensing connector pins add 0.1 ohm while the reference pin adds 0.01 ohms? You just forfeited ~1/2 degree of accuracy you paid for by adopting RTD in the first place.

Look, this is nit-picking in reality and there are bigger fish to fry when building a system. I am just pointing out that quality connectors should be used and cheap-o junk we often find on ama-ali-bay should be likely avoided in this application.

 

[passedpawn]

Well, that's not entirely accurate. What if the sensing connector pins add 0.1 ohm while the reference pin adds 0.01 ohms? You just forfeited ~1/2 degree of accuracy you paid for by adopting RTD in the first place.

Look, this is nit-picking in reality and there are bigger fish to fry when building a system. I am just pointing out that quality connectors should be used and cheap-o junk we often find on ama-ali-bay should be likely avoided in this application.

Ohms don't cause any errors on the sensing wires, and won't on the driving connections in a typical configuration (constant current). If there's no current, which is the case in the sensing signals, then there's no IR error.

I think it's germane to this discussion. Cheap connectors are OK if the right sensor is used. I believe the Auber sensors are 3-wire and mostly immune to the effects of a bad connector.

FWIW, I've got panel mount rtd connectors on my system.