Should the shields of grounded thermocouples be connected at the thermowell side and not at the logger side? I know that the shield should only be grounded at one end. The signal ground of the thermocouples should be connected at the logger end only. Is this correct? Thank you for your help and time.

Yours truly,
Gregory Li
Kingston ON
Canada

Good morning Gregory,

Your are quite correct in that the shield should only be connected at one end. Which end should not matter as long as only one end is grounded. I would try both ground and use the one that have lest noise.

Cheers,
Roger

I am not sure which ground to use for the different signals:

According to the scheme om page 148 of the manual I presume that

1. Gd of the serial channel is internally connected to Gd of the digital channels?
2. Analog out A0 is internally connected to analog Ground Ac?
3. 12V of serial channel should be used in combination with Gd of serial channel and thus is also internally connected to digital ground?

Regards,
Gerben

Good morning Gerben,

1. Gd of the serial channel is internally connected to Gd of the digital channels?

   Yes

2. Analog out A0 is internally connected to analog Ground Ac?

   No. The AO is the analog output of the DT800. The output is between AO and SR. The SR is the true analog grond and the AC is the Active Common

3. 12V of serial channel should be used in combination with Gd of serial channel and thus is also internally connected to digital ground?

   The shield should be connected to the Ch terminal. If you need to use a guard potential then it will be connected to the Gu terminal. Please refer to page 183 of the DT800 User manual

Cheers,
Roger

Thank you Roger,

Still one uncertainty:

Point 3. Here I meant the 12V= output at the Serial Channel block at the front of the DT800. Your reply relates to page 183 for shielding analog inputs. I want to know where to connect the negative pole, not necessarily the shield.

As the 12V= is meant to power external devices as a buffered voltage from the internal battery or connected external power supply I suppose the grounding therefore should be AC??? I don't know, because in the drawing on page 148 it is situated at the digital section.

Thanks again,
Gerben

Good morning Gerben,

The 12V is the supply voltage of the DT800 current limited with the return being the digital ground.

Cheers,
Roger