1756-IF16 Differential measurement anomalies

[glass123]

Hello, friends

my 1756-if16 differential connection, has been used again (almost 10 years), the measurement value of each channel of the entire module is small, the Fluke 715 process signal generator plus analog signal is also the same, the new module is still the same, the peripheral lines are removed is still the same, the front connector is also checked, the module configuration information is also checked.

As shown in the attached drawings, the open circuit of the line displays -24, with Fluke 715 given 20ma displays 24, shouldn't 20ma display 100?

 

[A_G]

Welcome to the forum! Just my opinion and some will disagree, but I always use Raw Counts instead of Engineering Units. I believe in your case the raw counts are 0 to 32767. Then I calculate mA from raw counts in the ladder logic

 

[glass123]

Thanks to A G, this problem is caused by the extension of the external line of a channel, and there are non-standard wiring problems in the extended part of the line, I plan to standardize the line connection first, maybe this method will not work, then, I plan to connect the single-ended module of the same device, depending on the use situation, I have replaced many spare channels on the single end, and no strange phenomenon has been found. Any new developments in the later period will be timely feedback。

 

[robertmee]

Welcome to the forum! Just my opinion and some will disagree, but I always use Raw Counts instead of Engineering Units. I believe in your case the raw counts are 0 to 32767. Then I calculate mA from raw counts in the ladder logic

Why use 32767? That's plc5 holdover. If you want a generic value use 4000 and 20000 always for every 4-20ma input. The channel data reads ma x 1000. Very useful for a tech to troubleshoot.

 

[glass123]

Welcome to the forum! Just my opinion and some will disagree, but I always use Raw Counts instead of Engineering Units. I believe in your case the raw counts are 0 to 32767. Then I calculate mA from raw counts in the ladder logic

Today, when checking, found a problem, the total 24V negative grounding of the power supply, 24V negative grounding on the differential and single-ended method has any impact? Will the software display the actual value too small?