Wrong temp reading

[marinechiller]

I have an Eliwell EWPC902T with a PTC probe. Actually 3 of them running different systems in identical setups. 2 are working perfectly. The third is giving me issues.

The temperature reading starts out fine when a new probe is installed. Over the course of 24 hours the reading creeps higher. 24 hours = approx 1.5°C higher each day.

As a result the temperature in the system gets lower and lower because the controller thinks it is too warm and keeps calling for more chilling.

I have replaced the probe with a new one out of the box and it still gives a false reading. I have also connected a probe from a different system and the reading was accurate, although I have not left it on there for long.

Would the controller be suspect here? It was used elsewhere some years ago, not sure of the exact history.

Marine CHiller

[Yuri B.]

Swap the "suspect" Eliwell with one of the two "honest" ones. Then you know for sure fault is in the controller and not in some connection.

[marinechiller]

I will try that. The other possible issue is that the probe is about 100m away from the controller. Anybody know the limit on distance between eliwell controller and ptc probe?

[marinechiller]

Tried switching controllers. The issue still exists. So, in summary,
1)the controller works perfect on the other systems
2)two brand new probes gave the same result
3)all connections have been re-wired

My only theories
1)100m with 4 connections (including ends) is too long of a run. Waiting on a reply from supplier for this answer OR on the wisdom of any of you here
2)When the wire was run, it got damaged and wet/salty air is degrading it noticeably each day?!?!

[Brian_UK]

Extract from Eliwell handbook, link below...

Fault signals - 'E1' = room sensor fault - check wiring & connections between control and sensor. If no fault in wiring, check sensor
resistance value as per table shown below. 'E2' = evaporator sensor fault - check as per E1.
Sensors - Eliwell controls predominantly use PTC sensors with NI100 & PT100 types also being used on some models.
Sensors - connections - preferably use screw connection blocks or spade connections.

Sensors - extension - PTC sensors are extendable to a max. of 100 mtrs using 1,5 mm square section conductor cable.
Sensors - interference - avoid running sensor leads close to other electrical equipment and other cables conducting large switching loads. If this is unavoidable, use screened cable, earthed at both ends.

Sensors - resistances - sensor temperature (degree C.) / ohms resistance

Q1, Are you using the correct cable?

Q2. Is it adjacent to power cabling?

Handbook link..
http://www.thermofrostcryo.co.uk/tec...ndbookv2.0.pdf

[cadwaladr]

i would solder all connections to the probe ,and use cable/wire that is at least twice the guage/size what are the other controllers probe lengths are they long ,if you are sure of the latter get crushed ice immerse probe into it should read 32/0 f/c,

[marinechiller]

To Brian_UK:

Q1, Are you using the correct cable?

Using AWG 22 works out to .33 mm² section. Good call Brian. Oops.

Q2. Is it adjacent to power cabling?

It gets crossed by cable powering 10hp heat pump. Wire is also not shielded.

Thanks for the handbook link.

To cadwaladr:
I like how you think. I have used the crushed ice method, also have a mercury thermometer to check against. Readings are definitely off.
The other controllers have shorter cables (about 30m and 50m)
Using larger cable is necessary according the Eliwell handbook - also good call.

So, current plan:
1)Replace cable with shielded 14 AWG
and possibly
2)Move controller closer