ADC measurements using CT63 (EGS5)

[info...@gmail.com]

Hi everyone,
i use the CT63 and measure the voltage of a distance sensor that is connected to ADC1_IN.

My code to get the value is like that:

ADC adc = new ADC(0, 0);
for (int i = 0; i < numberofmeasurements; i++)
 {
            //Get current voltage from adc
            values[i] =  adc.getValue();        
 }
 

My Problem is the measured values are not like i expected.

For testing i used batteries:
1,5V Batterie => measured value 61
6V Batterie => measured value 244

In the "EGS5 AT Command Set" Documentation i saw the following:
 

Measurement value
-25...+2425 Measured voltage in mV
Resolution: 1mV
Accuracy (typ.): 2mV
The captured value is the actual voltage applied at the ADCx_IN input. No further
calculation is required.

I think in the CT63 is some kind of series resistance who causes a voltage drop at the ADC channel. But i can't find any documentation about it. With the reduction of the measured values i lose accuracy, because my sensor has for every cm 3mV.

Has anybody else observed such a behaviour ?

[eppie]

The "EGS5 AT Command Set" Documentation is only intended as reference for the used EGS5 module inside the CT63 terminal. The EGS5 module is equiped with an ADC with a range of 0 - 2.4 Volt. Most likely the CT63 terminal analog input contains some resistors to extend its voltage range to a more practical one. (Like max 12V or 24V). Internal the voltage will be scaled between the 0 - 2.4V range. It this should not be the case you would already have blown up the ADC with the 6 volt battery. :-)

I guess that your multiplier is 40.

1.5V battery --> value 61 --> (61/40) = 1.525V
6.0V battery --> value 244 --> (244/40) = 6.1V

[info...@gmail.com]

Thanks for the answer.

You are right the limit of the CT63 ADC is 32V. I looked for the allowed voltage before i used the batteries.
Im no big fan of the "try and hope not to blow up" way.

I thought about something similar, that's the reason i mentioned the series resistance before the ADC.
Good to know that someone else have the same conclusion.

I already asked at www.ct63.de if there is any documentation about it, but i don't think i will get a answer from them.
Because if the multiplier has some tolerance it's important for me to know the range.

But maybe it's better we just use the EGS5. We have distances with max range 5m, that would be 500*3mV.
We just have to make sure if someone uses the device wrong that the voltage at the ADC don't go higher as 2,4V.