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common ground.

posted May 19, 2016 13:37:58 by Inge_Jeppesen
Why is it that thermistors and pressure sensors can't share a ground like Paul states many times. ?
Norway
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6 replies
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Dylan said May 19, 2016 17:21:01
Grounds can be shared. Signal wires are never shared and the 5v ref can be shared but never with thermistors.

Do you have SD Premium Inge?

This is a good video:

Section 9 The 5 Volt Reference Circuit (complete)

Belgium, Europe
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Inge_Jeppesen said May 19, 2016 17:24:18
I must have heard wrong. Will rewatch😊

Not subscribing yet... Want to but have not got the time.

Thanks.
Norway
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Chris said May 20, 2016 01:34:10
Thermistors are a pull down circuit is most cases, the ECM sends out 5v and the changing resistance of the sensor pulls it to ground. In a lot of cases the 5v ref is the monitored side of the circuit. The ECM protects it with a resistor to prevent it from shorting out. If you back probe the 5v ref wire with the sensor unplugged it will show 5v, plugged in it will read less depending on the resistance of the sensor.

Pressure sensors being 3 wire sensors can share a ground. They all have a 5v ref, ground and signal. The ref circuit should show 5v all the time, the ground should show less that .05 mv while plugged in and the signal should vary between .25 and 4.75. Hope this helps
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Inge_Jeppesen said May 20, 2016 05:03:08
Thank you.

Great feedback. I was sure I heard him say in one of his videos that "these can not share ground"

I was thinking it had to do with floating ground in some cases.

I will try to find it if I can so I can put in the link.

Inge.
Norway
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PaulDanner said May 22, 2016 12:07:34
Thermistors are a pull down circuit is most cases, the ECM sends out 5v and the changing resistance of the sensor pulls it to ground. In a lot of cases the 5v ref is the monitored side of the circuit. The ECM protects it with a resistor to prevent it from shorting out. If you back probe the 5v ref wire with the sensor unplugged it will show 5v, plugged in it will read less depending on the resistance of the sensor.

Pressure sensors being 3 wire sensors can share a ground. They all have a 5v ref, ground and signal. The ref circuit should show 5v all the time, the ground should show less that .05 mv while plugged in and the signal should vary between .25 and 4.75. Hope this helps


Great description Chris! Thank you
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PaulDanner said May 22, 2016 12:10:13
Great feedback. I was sure I heard him say in one of his videos that "these can not share ground"

I was thinking it had to do with floating ground in some cases.

I will try to find it if I can so I can put in the link


If i was talking about a floating ground it would have been related to a VRS and ones that use a floating ground cannot be shared.
Also there would be some issues with connecting your scope with multiple channels when connecting to one of these. Section 21 in my book
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