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Fraser Stewart avatar image
Fraser Stewart asked

Can someone tell me about resistance based sensors?

I would like to know about resistance senders.

I have some on my boat for water and diesel.

These are rated in Ohms. In my case from 0-190ohms.

For my Raspberrypi running latest Venus Os, with a new GX tank 140 I have the option between Voltage or Current.

But Current is in 4-20ma not in Ohms

Can anyone explain this to a noob. I dont know enough about this but hope someone can inform me and others


tank monitor
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3 Answers
Fraser Stewart avatar image
Fraser Stewart answered ·

I thought I would update people on this.

I was wrong to by this. Or had the wrong sales rep.

However there is a way.

Thanks to my dad who in a previously was a electronics engineer and is still a guru.

By adding a resistor of 270 ohms on the positive side signal cable we were able to turn that sender into a voltage based sender. At 190ohms creating 5v on a 12v line. Or 10volts on a 24v.

My sender now plugged into a gx tank140 will be seen as a voltage and can therefore display a very accurate value.

With different ohms senders you will require a different resistor.





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Joel Nordahl avatar image Joel Nordahl commented ·
Hi, do you have a drawing on how you did this. I'm trying the same and it's not really working. Would be great if you can tell me how you connected it. /Joel
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pwfarnell avatar image
pwfarnell answered ·

The GX Tank 140 either requires the senders to send a voltage signal 0-10V DC or a current, 4-20mA. The GX Tank 140 does not work with resistance based sensors. The Cerbo GX takes resistance based sensor inputs, not sure about the other Venus devices and no idea about the Raspberry PI.

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Fraser Stewart avatar image
Fraser Stewart answered ·

Well nobody who sells this product in the Netherlands seems to be aware of that. Both the company where gx tank 140 was purchased think it should work and the company that produce the sender claim that it should work.


Im confused really as i get readings, just not the full 4 to 20mA

More like

17 to 20mA


These Ohm senders are the industry standard here and as far as I was aware Victron are a Dutch company.

Mysteries stuff


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pwfarnell avatar image pwfarnell commented ·
Which is why the Victron Venus devices such as the Cerbo GX support resistance senders directly, the GX Tank 140 is an add on to the Venus devices for those people who do not have resistance based senders. On my boat I have a Cerbo GX, GX Tank 140 and voltage based sensors, so the 4 resistance inputs on the Cerbo GX are not used. There is no mystery here.


you are getting some readings because the resistance based sender is allowing some current to flow, just not the correct range. If the sender had a higher maximum resistance it would reduce the current more.

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Fraser Stewart avatar image Fraser Stewart pwfarnell commented ·

Ok. Thankyou


It makes more sense to me.


My fustration is not with your explanation but based on the lack of knowledge supplied by shops that sell Victron stuff in The Netherlands. I have been on the phone to the company who sold this to me and to the manufacturer of the sender who also sell gx tank 140 and both said that i should be able to use the gx tank 140 and this type of sender.

"you are getting some readings because the resistance based sender is allowing some current to flow, just not the correct range. If the sender had a higher maximum resistance it would reduce the current more."

So adding a resistor to the sender would give less current to the gx tank 140 and present less results



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pwfarnell avatar image pwfarnell Fraser Stewart commented ·
If you add a resistor then you may read 12mA to 15mA because it will increase both minimum and maximum resistance.


i now understand your frustrations if the suppliers do not know the equipment specs.

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