openinverter forum

I am using a CCS Type 2 connector which has PT1000 RTD temperature sensors on the DC and AC power pins.

What method do control units typically use to measure RTD sensors ?

I have used NTC thermistors before, consisting of a pull up resistor on an analogue input, but I have never used RTDs before.

Do control units use a special interface to measure RTD sensors, such as a wheatstone bridge or a dedicated IC designed for measuring RTDs ? Or do control units simply use a pull up resistor on an analogue input ?

I understand cost is an important factor in automotive, so thought control units would use the simplest and cheapest method to read RTD sensors.

The CCS connector states two temperatures thresholds:

• 80 degrees C to derate the charging current
  90 degrees C to stop charging

I looked at using a pull up resistor with an analogue input, but the problem is there is a very small difference in resistance:

• At 80 degrees C the resistance is 1308.97R
  At 90 degrees C the resistance is 1347.07R

Using a 1k pull up to 5V, this produces a voltage drop of:

• At 80 degrees C the voltage drop is 2.835V
  At 90 degrees C the voltage drop is 2.870V

This is a difference of 35mV which is going to be difficult to measure in a noisy environment (EMI).

There would also need to be hysteresis on each of the two threshold measurements which would be an even smaller voltage.

You could compare your sensor voltage to a 2.5V reference and then amplify the result. So basically v_out=(v_sens - 2.5) * 10

And you can have pretty low cutoff low pass filtering, like 1Hz to get rid of the noise

Thanks johu

I am using an off the shelf controller which has 0 to 5V analogue inputs, so cannot change the interface without designing and building additional hardware that sits outside the controller which I would like to avoid.

I am curious how these sensors are interfaced in automotive controllers seeing as the CCS type 2 connectors are common place and all use these PT1000 sensors.

Are they using a typical analogue input or do they have a special interface for PT1000 sensors ? Such as a wheatstone bridge or a fixed current source with a PGA (programmable gain amplifier) etc

A very typical CCS choice. Use something that is really expensive and doesn't fit the purpose Sorry for the rant.

https://www.adafruit.com/product/3648

It depends on the bits of your ADC? Is it 10 or higher?

I don't know if I would bother much with 80 or 90 degrees .
At 80 I would already stop charging I think. Especially if it rose rapidly.

Adding an cap will filter electronic noise and adding a mathematic model will make the conversion smarter .
Sample 4Hz and go with the 1Hz value etc

I would say more then 55 degrees is worth an attention to the user already. Cut off by 80?