Horstmann programmer

[gas4you]

Went to a heating fault today, well in fact 2 faults, 2 port zone valve failed and faulty programmer as above.

My main question on here, is that the programmer had intermittent buzzing noise and whilst buzzing I recorded fluctuating voltage of between 230 VAC and 1130 VAC.

As a simple gas engineer how could my multimeter be recording in excess of 1000VAC when the supply is only 240

It only gave these readings when it was buzzing.

Just curious to know how this could happen

 

[ericmark]

When working on the Falkland I was issued with an AVO meter for automotive use. When fitting two way radios it measured 50 amp on transmit through a 14/0.012 cable (about 2mm) which should have blown the 5 amp fuse and for that matter the cable as well. The RF was messing up the meter and when I measured it with a Fluke meter it showed the 3 amp it was really drawing.
I think something similar may be happening in the case you relate in when the relay or what ever is busing is making the noise it is also producing RF interference which is messing up your meter. It is referred to as EMC and some meters are not very good at rejecting this.
I will not say cheap as the AVO meter I was using was not cheap.
Eric

 

[Softus]

My main question on here, is that the programmer had intermittent buzzing noise and whilst buzzing I recorded fluctuating voltage of between 230 VAC and 1130 VAC.

Was it by any chance it this guy's house?

http://www.diynot.com/forums/viewtopic.php?t=149506

 

[gas4you]

No, I'm glad it wasn't.

 

[Keith77]

Its quite possible to get a high voltage if there is an inductive load and the supply is rapidly switched on and off (buzzing noise may indicate this is happening). The back emf as the current through the inductor is turned off can be a lot greater than the voltage under load.