[Stickman42]

I have a Nortec NHMC030 steam humidifier at my workplace. There is a Nortec sensor wired in that reads the humidity in the room. The value is displayed on the main unit, and the unit cycles on and off as necessary. Recently, the sensed value swings wildly. I have checked the connections and all seems OK there. The sensor is about 13+ years old, so I guess it may need replacement.

The replacement Nortec control is over $600. Since this is only used to read humidity, I'm wondering if there are any other less expensive options.

 

[supers05]

Have you verified with a hydrometer if the sensor is accurate? At least a dry bulb/wet bulb measurement? There may be another problem other then the sensor. (yearly maintenance is required on those units)

The sensor is a far better option, but if you really wanted to go with a plain Jane humidistat, then it would be wired in series with whatever else is wired between terminals 8/10. Remove the sensor from 26/28/30/32.

FYI:
http://www.humidity.com/m/0/06-172-nh-installation.pdf

Cheers!

 

[Stickman42]

I do have an analog (dial) hydrometer in the room and it does remain consistent with the sensed RH. The problem is that when the room reaches the RH set point, the sensor reading will inexplicably drop about 25F, causing the unit to go right to full output unnecessarily. A few seconds or minutes later, the sensed value will rapidly rise back to the correct RH. To me, this points to the controller.

With regard to the maintenance you mention, I'm assuming you mean unit maintenance and not sensor maintenance? I do replace the steam cylinder as needed and clean/repair/replace the drain and fill valves regularly.

Thanks for the control options. I thought a humidistat was possible. But does that make it a less desirable way of operating versus the modulating controller?

 

[supers05]

Yes i meant the humidifier, not the sensor. Sounds like you're already doing that. Those drain valves actually come completely apart for cleaning.

You'll have larger swings between the off and on cycles with a humidistat. To compensate, you can adjust the maximum limit in the control to slow the humidifying down. It'll be trial and error. In my experience, they are grossly oversized. I start at 80% and make sure it cycles off after 30 min or so. The longer the cycle, the better the comfort, but it still has to keep up. PG. 11 in the above manual. The swings will be different for every humidistat, but 5-10% is fairly normal. (for example if set for 45%RH, then it'll typically engage at 40-43ish% and off at 47-50ish%)

Check the control wires on the controller/sensor. You might have a loose/corroded wire. If you have a multimeter, check for continuity from end to end, and for shorts between wires. If that doesn't work, then yes maybe the sensor is FUBAR.

Cheers!

 

[Stickman42]

I spoke with Nortec support and between the two of us we couldn't identify my existing sensor. Pictures of outside and inside front plate attached. As you can see, there are no buttons or display. i.e. it's just a sensor. Nortec recommended going with their model # 151-0142, picture attached also. What's confusing to me is that they are recommending a humidistat, and not a sensor. Won't that cause a conflict with the setpoint controls on board the NHMC itself?

 

[supers05]

If it's a communicating one, it will work just the same as you have. If it's a regular bi-state (digital, on/off) then the setpoint will be ignored.

I'll look up that model later tonight.

Cheers!

 

[Stickman42]

Update - I purchased a model 151-0142 and installed it with Nortec support's assistance. Other than the wiring, there were two parameters that needed changing in service mode on the unit. The way to get into service mode isn't mentioned in the IOM. I had to get that from Nortec. The setpoint control is now done with the humidistat. Bottom line - all seems to be working. Thanks for your help!

 

[supers05]

Awesome

Cheers!