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3 wire gauges, how to connect and calibrate them.

With the Alba Combi you can easily connect to almost any 3 wire analogue gauges,  those gauges have typically 3 wire connections, they are identified as supply, sensor and ground. The ground is connected to the minus terminal of the battery, the supply is connected to the plus terminal of the battery when the engine is turn on, and the sensor line is connected to the sender on the engine.

In order to convert from the analogue readings to NMEA2000 we have to measure the voltage between ground and supply line and from ground and signal line, voltage in the supply line is either 12 or 24V and voltage in the sensor  line is a variable voltage between 0V to around 6V.

The voltage in the sensor line is used to apply the calibration table which will give us our digital reading, and the supply voltage is used to correct the reading for different battery voltage, that is only needed with the unregulated VDO and similar type gauges, if you use a Faria or any other regulated sender, this connection will not be needed.

Dibujo1

 

This is a typical connection for a 3 wire gauge, supply is read on channel 7 (pin29) and sensor voltage is read on channel 12 (pin 35), ground is connected to pin 36, all grounds are common so is not important what ground yo connect to.

With those connections done you have to calibrate, below is the calibration table required for the above connection.

calibracion AC

 

 

You have to select the correct sensor and activate the correction voltage only if your gauge is unregulated.

You may change the calibration table afterwards if any adjustments are needed on the correction.

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