Hello all.
I’m trying to add a GX tank 140 to a boat with existing capacitance sender (VDO N02-240-404 - 4 to 20mA).
In the current installation the sender is connected to ground on one side and to the gauge on the other. (see drawing), but the 140 need both wires form the sender to be connected (see drawing).
Unfortunately, it is not possible for me to run both wires from the sender to the 140. is it possible to wire the 140 so that the measurement will be referenced to ground?
Thanks,
You can not easily have dual gauges on a 4-20mA system. The system applies a voltage to the sender which controls the current passing through the system. You can not have 2 gauges in parallel trying to drive the sender.
You may be able to have a second current sensor in series with this device as per the marked up sketch of both devices. The negative wire from the sensor is disconnected from the negative battery wiring and fed through the GX Tank 140 and then back to the negative wiring. This will add an extra resistance into the circuit for the GX Tank 140 measurement, the existing driver may be able to account for this, it may not, therefore I am not 100% sure it will work or not. It should not damage anything if it does not work, but it is at your risk.
There are also 4-20mA signal splitters. I have seen these used industrially where a signal needs to go to 2 controllers but not sure about in a boat or vehicle with this type of sender. Just Google for 4-20mA signal splitter.
Thanks for the detailed response @pwfarnell
I did not know you can (theoretically) connect 2 gauges in series.
My situation is a bit different, i’m not looking to connect the old Gauge and the 140 at the same time.
In my installation, the sender is on one end of the boat, and the gauge is on the other, I want to install the 140 to replace the Gauge. The issue is that I cant run another wire from the sender to the 140. I only have the “G” wire that is currently is connected to the Gauge, the other wire is connected to boat ground.
Sorry for the misunderstanding. The system shown below MAY work. The ground connection for the sensors are isolated from the rest of the GX device. However, without knowing the exact details it is not guaranteed and risk will be yours to accept.
The other proviso is that it will only work AS LONG AS you only have one tank you want to connect because the GX Tank 140 has a common ground and you are using the common ground as part of the signal path.
The manual states
The USB cable is electrically isolated from the sensors, as such there is no risk of ground loops occurring between the sensors and the USB socket of the GX device.
The “GND” connections of all four channels are internally connected, they are not individually isolated from each other.
The other possibility if you have a voltage source close to the sender is to connect that to the sender, use your single wire to come back to the GX Tank 140 and then connect the gnd on the Tank 140 to a local ground. This would better for the Tank 140 but I do not know about the sender.
Thank @pwfarnell this is extremely useful.
