Mathematical calculations

[haskle]

I have tried to follow the Help section & previous topics, but I am still stuck ...

In order to calculate the current volume of oil in a horizontal cylindrical tank I need to process several mathematical calculations in turn. Rather than try to do everything in one go, I have broken these down in to series of discrete "sums" using function nodes. So far so good.

But I can't work out the syntax to put in a function Node d manipulating the output of two others, eg, "the result of function Node b minus the result of function Node c "

How might I phrase this? I am not sure how to identify the previous output of a function node and put it in to another node for further processing.

Many thanks!

[gerry]

Sounds like you may want to look at saving values then pull them back in when you need them. Look at using flow.save , you should find this in node red docs.

[dceejay]

You may also want to look at node-red-contrib-tank-volume - npm as it may help

[jbudd]

You can join the outputs of the two function nodes with a join node like this

[{"id":"c48f46e577eaf844","type":"function","z":"a3e369ffd4e1629e","name":"","func":"msg.payload = 27;\nmsg.topic = \"topic1\"\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":340,"y":120,"wires":[["6c4f6e5cbee8072a"]]},{"id":"3a263e81ac6bd039","type":"function","z":"a3e369ffd4e1629e","name":"","func":"msg.payload = 5;\nmsg.topic = \"topic2\";\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":340,"y":160,"wires":[["6c4f6e5cbee8072a"]]},{"id":"6c4f6e5cbee8072a","type":"join","z":"a3e369ffd4e1629e","name":"","mode":"custom","build":"object","property":"payload","propertyType":"msg","key":"topic","joiner":"\\n","joinerType":"str","accumulate":false,"timeout":"","count":"2","reduceRight":false,"reduceExp":"","reduceInit":"","reduceInitType":"","reduceFixup":"","x":490,"y":140,"wires":[["398e5fefd1268494","3c35d0d4665504b7"]]},{"id":"398e5fefd1268494","type":"function","z":"a3e369ffd4e1629e","name":"","func":"msg.payload = msg.payload.topic1 + msg.payload.topic2;\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":620,"y":140,"wires":[["7aad460a950c31d3"]]},{"id":"2469c14de3faaafc","type":"inject","z":"a3e369ffd4e1629e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":200,"y":120,"wires":[["c48f46e577eaf844"]]},{"id":"3dbb85870f589efb","type":"inject","z":"a3e369ffd4e1629e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":200,"y":160,"wires":[["3a263e81ac6bd039"]]},{"id":"7aad460a950c31d3","type":"debug","z":"a3e369ffd4e1629e","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":770,"y":140,"wires":[]},{"id":"3c35d0d4665504b7","type":"debug","z":"a3e369ffd4e1629e","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":630,"y":100,"wires":[]}]

And the node @dceejay mentioned is introduced here

[Colin]

Put the calculations one after another, not in parallel. Then it is much easier.

[drmibell]

"Great minds" think alike. I had this all set to post, honest.

[{"id":"754ed93fca304316","type":"inject","z":"1a062a4d47b6ea5b","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":200,"y":1140,"wires":[["0de4747b872883fb"]]},{"id":"0de4747b872883fb","type":"function","z":"1a062a4d47b6ea5b","name":"","func":"msg.a = 27;\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":340,"y":1140,"wires":[["540bb50f4da2ae71"]]},{"id":"540bb50f4da2ae71","type":"function","z":"1a062a4d47b6ea5b","name":"","func":"msg.b = 5;\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":480,"y":1140,"wires":[["251b9bc5bc098a8b"]]},{"id":"251b9bc5bc098a8b","type":"function","z":"1a062a4d47b6ea5b","name":"","func":"msg.payload = msg.a + msg.b;\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":620,"y":1140,"wires":[["57e15183b4acee15"]]},{"id":"57e15183b4acee15","type":"debug","z":"1a062a4d47b6ea5b","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":770,"y":1140,"wires":[]}]