Overview of the RSC-HMU Controller Fuel Level Circuit

The RSC-HMU sender circuit takes a 0-5V input into the UA3 input on the D sub connector. The Signal should be connected to UA3P and the 0V to UA3N. 

Activating the Fuel Level Sensor and Setting the Tank Size

This can be done on the module commissioner page. Set the fuel tank size, the fuel type to diesel and the fuel level box should be checked. Hit "Save as Defaults" to save the page.

Checking the readings in the controller

One set you can check the readings in the controller. For this you should visit the RSC-HMU Telemetry page. here you can see all the readings from the sensors. You can see from the below screenshot the fuel level line. This line shows the Input "Mux 2", Title "Fuel Level", Tank Level in L and finally the sensor reading in LSB (Lowest Significant Bit - Essentially the analogue voltage converted to a digital signal.) in the controller, at a signal of 0V, the sensor should give a signal of around 93 LSB. At 5.6V it would be around 1023 LSB. The fuel level in the tank is calculated from this LSB reading.

It is updated around every 15 seconds, so after changing the input it may take a few seconds to appear and then recalculate the tank level.

Troubleshooting the Tank Levels

1) Check the Sender

You should check the output from the sender is correct, showing 0-5V DC. if the tank is half full, it should be showing about 2.5V. Note: If there is any issue with the tank, this can effect the sensors reading and is a separate issue. If the sender isn't outputting a reading at all, or isn't correct, change the sender.

2) Check the Sender Wiring

Its possible something has damaged the sender cables; either mechanical, human or animal damage could cause a break int he cable. Check the cable and replace as necessary. 

3) Check the controller

Wiring another sender into the controller to check it can verify if the controller or the gauge that is an issue.

4) Tank Empty Level

You can change the tank empty 

5) Calibrate the tank sender

You can edit the Controller Calibration Table in SQL Lite to change the high and low calibration values to match the values you see in the controller. See the article "Changing the fuel sensor calibration on the RSC-HMU Controller."