NMEA 2000 Engine Monitoring

[Fuss]

Thanks, you could be right that taking inputs off the original signals but, thinking about this, I’m not sure this is right…for example.
If you run multiple analog instruments off one sensor, then both instruments read wrong, you have to change the sensor to one for two instruments. I am not sure the nmea2000 will affect analog instruments the same as adding a 2nd analog instrument.
I hope I wrote this clearly enough…does anyone have experience of what the original gauges read when a nmea2000 converter box is connected to the same wires?

[SV-Apres]

Originally Posted by Fuss

Thanks, you could be right that taking inputs off the original signals but, thinking about this, I’m not sure this is right…for example.
If you run multiple analog instruments off one sensor, then both instruments read wrong, you have to change the sensor to one for two instruments. I am not sure the nmea2000 will affect analog instruments the same as adding a 2nd analog instrument.
I hope I wrote this clearly enough…does anyone have experience of what the original gauges read when a nmea2000 converter box is connected to the same wires?

lets take a temp or oil pressure sensor as an example, it is just a resistor that changes resistance with temp or pressure.

in the analogue system:
BatV ------ GaugeR ----- sensorR --- (ground through engine)

the gauge is a coil with a fixed resistance, the sensor is a variable resistance.

in the CX5003, I expect it is a voltage divider circuit as shown below:
SensorSupplyV -------R1--------SensorR -----(ground through engine)

The voltage is sensed between the fixed resistor (R1) and SensorR and this voltage is used to assess Pressure or Temp.

I did not test the SensorSupplyV but this may not be battery voltage, it may be 5v or 3.3V - this would be problematic if you connected the analogue system to the CX50003 system.

also, if they were the same voltage you would have resistors in parallel like below:
BatV -------------- GaugeR ----- sensorR --- (ground through engine)
SensorSupplyV -------R1---/

So if the were connected together at the sensor connections then there would be 2 Resistors in parallel and the and both numbers would be wrong. however, if you are concerned with changes in reading vs absolute, this may be acceptable - you would have to do the math to establish if the additional resistor reduces your ability to sense in part of the range you need to sense