Ian wrote:
Hello Group
Help!
I am advised by manufacturer (Danfoss) that I should use 1.00mm2 two
solid copper core cable to connect their remote sensor to a TP7000M
prog roomstat and that the cabling must not be in close proximity to
any mains cabling.
The original cabling (1mm T&E, earth not connected) ran very close to
mains cabling. This caused wildly fluctuating temperature sensing (as
much as 5 degrees C on consecutive readings,which seem to be taken by
the controller at one minute intervals)
I have now re-routed the cabling to be , for the most part, 8-12
inches from any mains cable. I have used the 1mm T&E again. The
situation is considerably improved but I am still getting fluctuating
readings albeit more in the +- 1 degree C range. If I run a shortish
(about 1 metre) length of cable to the sensor absolutely nowhere near
any mains cabling the temperature readings are totally steady.
Since a reading even 0.5 degree below 'actual' temperature results in
a call for heat which then operates the zone valve and fires the Oil
boiler, the next reading may be at a heat higher than target and shuts
down everything, I can be left with the boiler running in bursts of
1 minute. I would like to avoid this if possible.
Any ideas on any appropriate cable to use - perhaps screened in some
way - or would some form of twisted pair help in any way? Is there any
1mm2 two core twisted pair available?
I'd like to resolve this before replacing
floorboards/redecorating.......
Many thanks for any input
Ian
Please reply to group - email address is not monitored
Ian

Just a thought Ian, turning the problem around, do you have any dimmer
switches or any other thyristor/triac controlled devices connected to
your mains?

Some of these devices, if inadequately decoupled for RF, can put very
sharp spikes onto the mains. These spikes, being radio frequency (RF),
can easily couple into nearby wiring either capacitively or inductively.

If the controller is high impedance and, in turn is poorly decoupled,
the spikes could upset things.

In the old days of dial-up telephone connections to the internet, I was
scratching my head as to why my connection was slow and unreliable on
early winter mornings. My wife never had problems. Then it dawned on
us:- I would invariably put the main light on via the dimmer, but my
wife would always put on a standard lamp or two. In the evenings there
was no problem because she always had her way - lighting wise! We
switched the dimmer off and my problems disappeared. I had run the
telephone cable too close to the mains wiring and it was coupling into
the modem and causing havoc.

Maybe a red herring but just an idea worth checking.

HTH

Steve.