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Coolant sensors... How many connections is too many?
StuartBJ - 7/11/11 at 05:29 PM

Hi Guys,

My megasquirt uses one coolant sensor, my electric water pump uses a coolant sensor and my digi dash needs a coolant seanor...... Now can I just use one or will each need it's own dedicated sensor for some reason? Voltage drop perhaps?

Im happy to use just one but will I get any headaches if I 'split' the signal?

Any thoughts welcome

big-vee-twin - 7/11/11 at 05:47 PM

I have three just like you will need.

MikeRJ - 7/11/11 at 06:07 PM

quote:
Originally posted by StuartBJ

Im happy to use just one but will I get any headaches if I 'split' the signal?

Any thoughts welcome


You are certain to get many headaches unless the following conditions can be met:

1) All devices are using the sensor in the same circuit configuration, e.g. one side grounded, or one side to a reference voltage.
2) All devices use the same reference voltage for the sensor.
3) All devices can be calibrated to the different temperature/voltage curve that will result from connecting multiple bias sources. This may be impossible as multiple bias resistors will shift the operating point into a non-linear region. You may be able to remove the bias resistors a from two devices and just rely on one resistor in one device.

Alternatively you could make a circuit to use you own bias resistor and have three buffered outputs, each with the required voltage range, but you would still need to calibrate the devices that are no longer using their native sensor.

Once you have ensured this, you now have a single point failure that can affect three systems that were previously all independent.

There is a good reason the production cars use multiple sensors...

wilkingj - 7/11/11 at 06:20 PM

quote:
Originally posted by MikeRJ

You are certain to get many headaches unless the following conditions can be met:

1) All devices are using the sensor in the same circuit configuration, e.g. one side grounded, or one side to a reference voltage.
2) All devices use the same reference voltage for the sensor.
3) All devices can be calibrated to the different temperature/voltage curve that will result from connecting multiple bias sources. This may be impossible as multiple bias resistors will shift the operating point into a non-linear region. You may be able to remove the bias resistors a from two devices and just rely on one resistor in one device.

Alternatively you could make a circuit to use you own bias resistor and have three buffered outputs, each with the required voltage range, but you would still need to calibrate the devices that are no longer using their native sensor.

Once you have ensured this, you now have a single point failure that can affect three systems that were previously all independent.

There is a good reason the production cars use multiple sensors...


Yep, I agree with that.

You cant just wire up three inputs to one sensor (Well you could... BUT...), its recipe for some "interesting" problems.

I wouldnt do it. As said above, each circuit is set to match its sensor, leave it as it is.

Keep to this simple rule:-
"If it Aint Broke - Dont Fix It"




PS... Stuart Can you put your approx location in your profile please.

[Edited on 7/11/2011 by wilkingj]

StuartBJ - 7/11/11 at 06:42 PM

Thanks chaps ...... 3 it is then