RMS solution for humidity 'control'

[Jeremy Wingate]

A simple but nice example of a basic control project that RMS was able to help a customer with. RMS is not a control system but this basic solution was suitable.

Customer Requirement
- Control a dehumidifier in a test area to ensure humidity remains below critical level. They could have used a HS5 / PF4 etc but they wanted to see the process in action if possible and didn't want to have a second probe in use if it could be avoided (already they had an RMS logger monitoring the room).

Solution
- RMS digital output module (RMS-DO-L-R) used and configured to trip dehum unit on when high %rh met.
- Monitoring probe configured with the room limits.
- Second measurement point made as a 'duplicate' of the live values (achieved using sum calc with only one input). Using this measurement point we could set a lower alarm limit to ensure dehum trigger before the %rh got too high.
- Tweaks to alarm levels and hysteresis band ensured smooth control (+/- <2 %rh)

Image showing
- Live %rh from monitoring probe (alarm limit @ 35 %rh) No alarms triggered during test!
- Duplicate of above reading (alarm limit @ ~32 %rh) Multiple alarms triggering relay
- Relay output (dehum unit on)
- Live temp from monitoring probe (not controlled by RMS)

[Emil Larsen]

Hi Jeremy

Very smart "concept" to just add a duplicate of a measuring point, with the sum calculator

The only requirements to the dehum is for it to have relay output that you put in the RMS-DO-L-R and is what makes RMS able to switch the relays on the dehumidifier. correct? :-)

[Jeremy Wingate]

We the dehum unit needs a switch inputr... this is tripped by the RMS-DO unit (i think that is what you mean anyway!)... I was pleased when i realised you could use sum calc with a single MPT otherwise the customer room alarms would have to match the dehum on off triggers or I would have to use complicated scripts.