Lead resistance compensation – Rockwell Automation 1771-IXE Installation Instructions User Manual
Page 13
Thermocouple/Millivolt Input Module
13
Publication 1771Ć5.64 - October 1998
Modules are typically calibrated at 25
o
C.
•
If the I/O chassis in which the 1771-IXE is operating is at
25
o
C, column A represents the maximum error for that
thermocouple type.
•
If the chassis operating temperature is less than or greater than
25
o
C, use the formula below to calculate the maximum error.
Maximum Error = Col-A + (
∆
T x Col-B)
Where: Col-A = the value from column A
∆
T = the I/O chassis operating temperature minus 25
o
C
Col-B = the value from column B
For Example:
If the I/O chassis is operating at 60
o
C, and a Type J Thermocouple is being used, then:
Maximum Error = Column A + (
∆
T x Column B)
= 0.78+ [(60 - 25) x 0.0423]
= 0.78 + (35 x 0.0423)
= 0.78 + 1.4805
= 2.2605
o
C
Millivolt Range Accuracy
Millivolt
Range
Max Error
@ Calibration
Temperature (25
o
C)
Millivolt Drift
-100 to 100
+8.85uV
+3.856uV/
o
C
Radiated Noise Susceptibility
Radiated Noise
Susceptibility Error
300-1000MHz Circular Wave, Field Strength = 10V/M
< +1%
Allowable Distances
The open thermocouple detection circuit injects a current of
approximately 7.3 nanoamps into the thermocouple cable. A total
lead resistance of 1370 ohms (685 ohms one–way) cable resistance
will produce +1 count (10uV) of error.
Lead Resistance
Compensation