I have a system where there are 8 inlet pressure measurements from 8 different channels. In my system, I am trying to maintain the pressure in a range using hysteresis. Here, I want the compressor to switch on even if one of 8 pressure measurement drop below a certain value (say 0.2 bar). But, I tr…

I assume you receive 8 different messages, node-red handles a single message at a time, you can combine the messages using a join node. Or use context to keep track of all values and compare.

I used global context to assign the output to a varuiable and used it for control. Thank you. But when I use join node to form an array of the 8 inputs, how can I check if at least one of the input is 1 or ON??

Don't use array mode on the join node, use key/value mode. Then it's a simple case of logic in a function node. There’s a great page in the docs that will explain how to use the debug panel to find the right path to any data item. Pay particular attention to the part about the buttons that appear …

If you already have the 8 channels and 8 hysteresis nodes set to provide a 1 if they need to be switched on then you don't need anything fancy, as any node outputting a 1 should be aa signal to act - not matter where it comes from... so just wire all of them into a node that just looks for a 1... …

[image] dceejay: am I missing something ? Possibly there needs to be a way of getting back to zero again when none of the inputs is on.

Presumably you would run for a timeout. You wouldn’t want to oscillate a compressor on/off around a set point

[image] dceejay: You wouldn’t want to oscillate a compressor on/off around a set point Hence the hysteresis nodes.

Ithank you very much for the replies. Though I found a method, I happen to have better understand on how to improve it. I thought having multiple inputs to one node to switch on the compressor might have contradicting signal. When I instead of having one particular output node, had 8 separate nodes…

I could not reply to you as I had met with an accident and was not able to work! Thank you for answering anyways and I found that my flow had an issue may be due to the node red version of it (v0.17.5). Multiple inputs with opposite values for eg: 0 and 1 are the inputs to the particular node with…

Help needed with comparing inputs using msg.topic

General

Colin 16 October 2021 14:30 10

I don't understand what you mean. Can you post the flow for what you have so far please so that I can better understand? So from the pressure inputs through to the compressor output. See this post for how to post your flow - How to share code or flow json

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Help needed with comparing inputs using msg.topic

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