Rockwell Automation 1762-IR4 RTD/Resistance Input Module User Manual
Page 63
Publication 1762-UM003A-EN-P - February 2003
Module Data, Status, and Channel Configuration 3-29
Calculating Module Update Time with Autocalibration Enabled
The following example illustrates how to determine module update
time with autocalibration enabled.
EXAMPLE
zews
Two Channels Enabled with Cyclic Calibration
Channel 0 Input: 100
Ω
Platinum 385, 1.0 mA source with 60 Hz Filter
Channel 1 Input: 100
Ω
Platinum 385, 0.5 mA source with 60 Hz Filter
From Table 3.15, Channel Update Time vs. Filter Frequency, on page 3-27:
1. Calculate Module Update Time without an Autocalibration Cycle
= Ch 0 Update Time + Ch 1 Update Time = 53 ms + 53 ms = 106 ms
2. Calculate Module Update Time during an Autocalibration Cycle
Channel 0 Step 1 (Module Scan 1)
= Ch 0 Update Time + Ch 1 Update Time + RTD ADC Self-calibration Time = 53 ms + 53 ms + 103 ms = 209 ms
Channel 0 Step 2 (Module Scan 2)
= Ch 0 Update Time + Ch 1 Update Time + Current ADC Self-calibration Time = 53 ms + 53 ms + 103 ms
= 209 ms
Channel 0, Step 3 (Module Scan 3)
= Ch 0 Update Time + Ch 1 Update Time + Current Source Calibration Time = 53 ms + 53 ms + 53 ms = 159 ms
Channel 0, Step 4 (Module Scan 4)
= Ch 0 Update Time + Ch 1 Update Time + Ch 0 Lead Compensation ADC Calibration Time
= 53 ms + 53 ms + 130 ms = 236 ms
Channel 1, Step 1 (Module Scan 5)
= Ch 0 Update Time + Ch 1 Update Time + Ch 1 RTD ADC Self-calibration Time
= 53 ms + 53 ms + 103 ms = 209 ms
Channel 1, Step 2 (Module Scan 6)
= Ch 0 Update Time + Ch 1 Update Time + Ch 1 Current ADC Self-calibration Time
= 53 ms + 53 ms + 103 ms = 209 ms
Channel 1, Step 3 (Module Scan 7)
= Ch 0 Update Time + Ch 1 Update Time + Ch 1 ADC Self-calibration Time
= 53 ms + 53 ms + 53 ms = 159 ms
Channel 1, Step 4 (Module Scan 8)
= Ch 0 Update Time + Ch 1 Update Time + Ch 1 Lead Compensation ADC Calibration Time
= 53 ms + 53 ms + 130 ms = 236 ms
3. Calculate Total Time to Complete Autocalibration Cycle
= (Channel 0 Step Times) + (Channel 1 Step Times)
= (209 ms + 209 ms + 159 ms + 236 ms) + (209 ms + 209 ms + 159 ms + 236 ms)
= 786 ms + 786 ms = 1626 ms = 1.626 seconds
After the above cycles are complete, the module returns to scans without autocalibration for
approximately 5 minutes. At that time, the autocalibration cycle repeats. If both cyclic autocalibration
and lead wire compensation (see page 3-30) are enabled, the two functions run concurrent to one
another.