LJlogM 1.05 - Resolution at 500°C

2 posts / 0 new

Fri, 04/07/2017 - 11:39

sjonatan

Hi, I´m using LJlogM 1.05 to acquire thermocouples type k. The temperature goes from room temperature up to 600°C. I noticed that when the temperature cross the 500°C the, application send and instantaneous error of -9999.

The hardware configuration is:

- T7-Pro + Mux 80 + 4xCB37

- Thermocouples: 10 untis, type K, Insolated, connected in differential mode with 100kohms (-AIN to GND).

- Cold Junction: LJ34CAZ (AIN 84)

- PChannels: 0,2,48,49,50,80,81,100,101,102

The constants_json configurations are:

--AIN#_RANGE : 0,1

-AIN#_RESOLUTION_INDEX: 12

-AIN#_NEGATIVE_CH: #+8

-AIN#_EF_INDEX: 22

-AIN#_EF_CONFIG_A: 1

-AIN#_EF_CONFIG_B: 168

-AIN#_EF_CONFIG_D: 55,56

-AIN#_EF_CONFIG_E: 255,37

The problem occurs randomly in different channels when the temperature cross the 500 value. For example take note of the following registers each 3000 (ms) intervals

499,825348

499,355316

499,124908

498,800201

-9999

500,029999

499,83609

499,470184

499,458282

499,377594

499,741119

500,019196

Please, may you help me?

Thank you in advance

Fri, 04/07/2017 - 14:23

LabJack Support

K-Type thermocouples should

K-Type thermocouples should work up to ~1300 K. It looks like the problem might be related to the cold junction compensation. A couple things to look into.

Try settings the CJC back to the default; CONFIG_B = 60052. That will use the CJC sensor on the T7's PCB. It may introduce some errors in your readings, but it might tell us where the problem is.
You can read the other result registers READ_B, C, and D to get the values that are used during temperature calculations. That might help us figure out where the issue is.