Module Update Time; Section 4.3 Input Image File; Input; File - Spectrum Controls 1769 User Manual

4-8 Compact™ IO Isolated RTD/Resistance Module
Section 4.3

Input

Image File
User's Manual Pub. 0300241-01 Rev. A

Module Update Time

The module update time is defined as the total time required for the module to sample
and convert the input signals of all enabled input channels and provide the resulting data
values to the processor. On an isolated module with one ADC per channel, all channels
convert the signal in parallel so the module update time is equal to the slowest channel
update time. When lead compensation is enabled (default setting) one out of six channels
in each module scan has both the RTD/resistance voltage measured AND the lead
compensation voltage measured. This repeats in a round robin fashion cycling through
all enabled channels. An internal multiplexor in the ADC switches between measuring
the lead voltage and RTD/resistance voltage. This switching increases the settling time
for each measurement and the overall channel update rate increases to the slower update
rates listed in Table 4-6.
Channel update time is also dependent upon the input filter selection. Table 4-6 shows
the channel update times based on filter selection.
Channels enabled for different input types
Example 1
Channel 0 Input: 3-wire 100 Ω Pt 385 RTD with 4.17 Hz Filter,
Lead Compensation enabled.
Channel (1 – 5) Input: 3000Ω resistance with 10 Hz Filter
Lead Compensation enabled
Module update time with lead compensation enabled
= slowest channel update time
= 964 ms
All Channel enabled for 3 wire RTD
Example 2
Channel (0 – 5) Input: 3 Wire 100 Pt 385 RTD with 470 Hz Filter
Module update time with lead compensation enabled
= slowest channel update time
= 10 ms
All Channel enabled for 3 wire RTD
Example 3
Channel (0 – 5) Input: 3 Wire 100 Pt 385 RTD with 470 Hz Filter
Module update time with lead compensation disabled
= slowest channel update time
= 4 ms
The input image file represents data words and status words. Input words 0 through 5
hold the input data that represents the value of the analog inputs for channels 0 through 5.
These data words are valid only when the channel is enabled and there are no errors.
Input words 6 and 7 hold the status bits. To receive valid status information, the channel
must be enabled.
You can access the information in the input image file using the programming software
configuration screen. For information on configuring the module in a MicroLogix 1500