Al avatar image
Al asked

Non linear Tank Level Sensor - Cerbo

I have a KUS 0-190 Ohm tank sender for a 1900l tank connected to the Cerbo, but the fluid level display is very stepped (changes every 60l or so), it's not very linear like the last installation with the same make of sender and a Cerbo I did before.

This time though, the tank is 25m away from the Cerbo and I used 0.75mm cable. The manual doesn't mention what cables to use, could 0.75mm cable be an issue for a resistive sender over this length?

cerbo gxtank monitorsender
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Justin Cook avatar image
Justin Cook answered ·

Certainly it could be an issue; a 0.75mm diameter cable (assuming copper) over a 50m round-trip distance has a resistance of 1.9 Ohm at 20C (would obviously be higher resistance at higher temperatures if the wire is running through an engine room or other high-temperature area), which could certainly result in skewed behavior in the Cerbo's readings - basically that length of wire has so much resistance itself that you're losing the resolution of your resistive tank level sender. If you meant 0.75mm2 cross-sectional area, then that's a little better at around 1.1 Ohm over that distance at 20C, but between the resistance of that length and the resulting voltage drop in power to the unit, I think you'll likely need to size up your cabling to it unless you can live with the lack of resolution.

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Al avatar image Al commented ·

Thanks @Justin Cook

Yes I did mean 0.75mm2 - 2 core cable! :)

Having a closer look at the graphs for the other KUS Resistive tank sender install with 1.5mm2 - 2core cable over just a 3m length, it also has stepped graphing. Although seemingly averages at 2% changes, whereas the newer install averages 3-5% steps rather than a linear state change.

I noted the empty and full resistances for the new install, so set the new tank 0% at 1.9r and 100% at 165r

I guess the stepped graphs could be friction on the float, 'sticking', if not the cable resistance, unless it's part of the algorithm that decides the next volume change increment?

I'll try to check the resistance as shown in tank setup on the Cerbo whilst draining the tank, to see if the resistance is mirroring a 'sticking' float or actually linear.

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