Vitodens O.A. sensor

Kritz_3

A strange anomaly with my O.A. temp sensor, every once in a while when I go to check O.A. temp I will see a reading of -26.
Then it will ramp up to the correct temperature? The total run of wire to sensor is 40' of 16/2 shielded. I have not done a resistance test as of yet. Has anybody seen this behavior?
Thanks, Steve

Empire_2

Not sure about your particular control, but I have a Johnson Control #149, and only for a sec. do I see an Eronious reading. That's when I check set point not actual temp. Hope this helps.

Nron_9

sensor

sensors are based on resistance and changes in readings may indicate a short or poor conection or moisture in the the out side sensor

Mike T., Swampeast MO

16-2 with a continuous shield and the shield connected to ground? Whose cable Or did you run inside of metal conduit? When I asked at electric supply houses was again looked at like I came from another planet. Wound up using 16 gauge "speaker wire".

Since it's just a changing resistance, I believe it's rather prone to influence by outside electro-magnetic fields. Wire should be run in its own chase/conduit well separated from line voltage sources.

Kritz_3

Vitodens O.A. sensor

The cable is Belden, some extra wire from a sewerage plant project I was working on. The shield wire is not tied into ground, all I used
was the 2 wires not the 'drain wire'. Only 5" or 6" is exposed to the weather, just enough to make a drip loop before entering the house. I was just wondering if the sensor behaves like this when it is on it's way south? I was also wondering would I get a fault code if it was shorting out?

Mike T., Swampeast MO

Grounding and EMI with sensitive electronic devices still gets me somewhat confused, but why not connect the shield to the ground in the receptacle for the power unit? With the shield not grounded at best it can't drain stray current to ground and at worst might cause problems in the cable it surrounds.

Unknown

change the wire

from shielded to Non Shielded.

Kritz_3

Vitodens O.A. sensor

Thanks, I'll try the grounding first then if that has no effect I'll change the wire. But what would unshielded do for me? I understand that I might be building up a charge(static) would that have an inductive potential on the 2 inner conductors? What gets me is 99% of the time the reading it is giving me is dead on.
Steve

Unknown

dumping the static buildup

think of the zap when you run across the carpet and touch the light switch.... it is not constant.

every manufacture I deal with suggests standard 18/2 non-shieled standard thermostat wire for all thermisters.

Kevin_21

Steve
I assume when you say you are checking the outside temp on the display you are switching from coding address 009:000 to coding address 009:001 to check the outside temp. if so it is normal for the initial error in the reading. you will also get a strange reading on the boiler temp. when you go back to address 009:000

Kritz_3

Vitodens OA sensor

I have the display show O.A. in large read out (009:001) as
the starting point.
Steve K.

marc

sensor

try to viessmann in rhode island, we have had 1 randomly read a temp. that was way off from the actual, we checked everything, and i believe we replaced the vr-20 board. but to be sure call viessmann tech. service, excellent help, james brown, mike fox, 1-800-288-0667 marc.

Kritz_3

Sensor

Thanks, Just got off the line with Miles @ Viessmann. Confrimed that O.A. sensor was good, and the VR-20 board was to blame.
Thanks again, Steve K.