EEV sensor calibration

[flange]

So I sent a tech out today to look at an ice rink machine we installed a while back. one compressor was apparently frosted up all the way to the discharge valve. recip machine, electronic expansion valve on each circuit. machine has worked very well since the day it was started, but today, my guy finds the suction sensor about twenty degrees out of calibration, so system was running very low superheat. so my question is this...he calibrated the sensor to the board, but will this be a permanent fix, or will problems come back? is it time to replace the sensor? Thoughts? its the sporlan board, with the remoote keyboard display, dont know the numbers.

[Octopus]

Sometimes the sensors screws up the resistance and sometimes the board starts to go and it constantly varies the reading kind of like "decay" on electrical components after being exposed to radiation. I would watch the sensors resistance carried over a wide range or temps and then back to a "control" set temp and see if it varies from when you started... I would contact sporlan I'm sure they have some guidelines pertaining to a troubleshooting procedure.

[Phase Loss]

my opinion is if the sensor needs a 20* offset...it needs to be replaced.

[flange]

while i dont disagree, tis not the season to be yanking the charge out of a rink chiller to replace a sensor. so far it has maintanined perfectly. had someone stop by there on the way home today. just curious if anyone had any experience in failures of these sensors.

[crackertech]

my opinion is if the sensor needs a 20* offset...it needs to be replaced.

But it could also be the board as someone said but a sensor is cheaper
to try first.

[Dowadudda]

I'd first take the sensor off the input and compare the actual temp to a resistance chart for that sensor. And then I'd check the input making sure it is sourceing dc voltage right. If those leads are somehow compromised from control to actual sensor, that could also throw it off. You have to check all this. A lot of guys think this is magic and it's really not. Just electricity. LOL.

I think what most of the controls manufacturers recommend is that if a sensor has to be calibrated more than 6 degrees, that it's wise to replace. Having said that. You need to make sure he is sure he is reading the medium correctly and has authenticated with his own tools that indeed it's a bad reading.

I have an example for you. Lets say a guy installs a sensor right at the outlet of an evaporator coil in the Discharge Air Stream. And the reading you take is in the honeycomb on a multi deck refrigerated case. Your gonna be warmer by as much as 5 or 6 degrees.

[crackertech]

I would like to add that you need to put that sensor into ice water it should read close to 32*f that's were you should start then go on from their.

[Phase Loss]

tis not the season to be yanking the charge out of a rink chiller to replace a sensor.

I am wondering why would you need to pull the charge to replace a temperature sensor?

I work around these Sporlan EEV controllers often, our Targets use them on their mechanical subcoolers. All of the sensors are mounted outside the pipe's. While I have not had any of these sensors fail yet, I am familiar with other styles of sensor failures. As 4D's and Cracker said, plotting the sensor resistance against a temperature/resistance chart and making sure the board is outputting the proper signal voltages are solid ways of diagnosing sensors. along with ice baths or installing the sensor right at the board to eliminate cable issues.

[flange]

sensor is mounted in the suction piping leaving a flooded evap. not my design, but it is what it is. putting sensor in water bath gets us to 32, but we are running fifteen leaving the machine evap minus five. it was checked verse pretty good instruments, and as i said has worked really well for six months. the other thing is we laid an automation system over the plant for web access, and the thermometers, automation sensors and our instruments all match within reason. sensor is going to be replaced when we can sut it down, i was just curious if those of you who do this work everyday see many failures? also anyone see the superheat setting mysteriously change? had that on another minus twenty chilla. put it back and it never changed again.

[Phase Loss]

am I understanding this correctly?

you are unable to replace the sensor because it is inside the refrigeration pipe and would require the removal of the system charge?

but you were able to give the sensor a 32* water bath without removing it from within the pipe?

[Dowadudda]

In controls, I can tell you, I have done enough to say that, I use to think I was going nutso, when I would set something up and then go back on the job later and find it different. I would say to myself "I swear I had that done". It's not magic. It's not divine intervention. Somebody is foolin with it.

But you can't say that. Because everyone who was near that unit would say emphatically "I didn't touch it". No one tells the truth these days. I catch guys lying to me about just about anything and everything.

As for the sensor failures. Sensors fail periodically. SOme will last forever, some not. It can depend on it's environment it's place in. Heat. Humidity. Expansion/Contraction, Corrosives like bleach.

[flange]

no, it was not put in a bath, it is currently in the suction line. we have additional sensors installed for the bas as well as thermometers all over the place. there are reasons for this. the automation sensors are correct and match our high quality instruments. its possible that someone is playing but doubtfull, as they are deathly afraid of this machine. they wont even clean the strainer on the condenser water without telling me. While i know that sensors fail from time to time, these particular boards seem to do funny things on two diffferent sites. who knows, as i call it F.M....second word magic.

[Dowadudda]

Your sounding naive. Saying they are afraid to touch anything. You can't be serious. Look. I am not no slouch and been around, know my stuff. I have a lot of experience with controls. You have no idea how attractive the buttons and dials are for people.