Rif.: SCXI information

[FrankyCam]

It's the first time I work with SCXI platform. We have a SCXI 1000, a pc mio 64 AI, a 32 input SCXI 1102 and a terminal block 1303 to read 32 thermocouple signal. Now we have the possibility to buy a SCXI 1100 and a terminal block 1300. Are they able for Thermocuple reading? What is the difference with 1102 and 1100, 1303 and 1300 respectively?

Francesco

[FatBoyMonchi]

Hi FrankyCam,

let's start from the terminal blocks:

SCXI 1303 is designed for high accuracy thermocouple measurements, and has a more precise CJC Temperature Sensor.

The 1300 is fitted for IC Sensors and the 1303 for Thermistors.

Speaking about the modules, I read:

the SCXI-1100 is an inferior product to the SCXI-1102 in almost every way. The only reason a customer would use a SCXI-1100 over a SCXI-1102 is because of the following features not present in the SCXI-1102:

• Multiple Filter Settings (although when you change a filter on the SCXI-1100 it is applied to all channels at once, and it is jumper configurable). The 1102C has an always-on 10kHz filter, but the SCXI-1100 has a Bypass setting that can far exceed 10kHz.  The 1102 has an always-on 2Hz filter. 

• Additional Gain Settings (once again, all channels must share the same gain setting).

Reasons that the SCXI-1102 is better:

• The SCXI-1100 does not store calibration constants on board, so the module is less accurate overall than the SCXI-1102. You can compare the specs online on the Data Sheet linked below. The gain error and temperature drift error specs in particular are much less accurate on the SCXI-1100.

• The SCXI-1100 has poor common mode rejection. Thus when using the SCXI-1303 terminal block it must use a 10 ohm bias resistor instead of the 10Mohm bias resistor that should be used with the SCXI-1102. The SCXI-1303 user manual describes the implications of this, but basically the additional current flowing through the thermocouple will introduce a small offset error.

• In the SCXI 1100, all 32 channels are multiplexed into a single Programmable Gain Instrumentation Amplifier (PGIA) and jumper selectable lowpass filter.  As a result, when using a low bandwidth filter on the SCXI-1100, the settling time is slow when scanning multiple channels. This can cause large errors in the measurements if the channels are not given enough time to settle.  The SCXI 1102, on the other hand, offers gain settings on a per channel basis and thus provides better performance and higher sampling rates for thermocouple measurements.  

• The gains on SCXI-1102 and 1102C are programmable, so you don't have to worry about jumpers.  The filters are not programmable and cannot be disabled.

Hope it helps,

FBM

[FrankyCam · Accepted solution]

Thank you very much for your answer. I should say :'That's all'.

Thank you again

Francesco