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Eurotherms
Eurotherms come in a number of different configurations, namely crates with varying number of sensors. For typical baud rates, there is a limit to how much data can be communicated across a serial line. This have proven problematic in the past for configurations using 3 or more sensors. In the latest version of the IOC (3.0.0 at time of writing), the frequency of requests per sensor is inversely proportional to the number of sensors, so the overall request rate stays constant.
The reads are split between slow reads and fast reads. The slow reads are split into 5 blocks. When communicating with the Eurotherm, the IOC will query each block of slow reads sequentially along with a fast read. In other words, the read sequence for each sensor goes:
Read slow block 1
Read fast
Read slow block 2
Read fast
...
Read slow block 5
Read fast block
[Repeat]
The time taken for each block is defined as the variable SECONDS_PER_READ in .../ioc/EUROTHRM/iocBoot/iocEUROTHRM-IOC-01/st-timing.cmd
The with the SECONDS_PER_READ set to 0.08 this would mean each block takes roughly 0.5s per sensor; second per read [0.08] * (number of reads in a fast block + number of reads in a slow block [3 + 3]) * num of read. There are 5 blocks in total so all parameters are reread every 2.5s per sensor. On a 3 sensor crate this would be a temperature read every 1.5s and a refresh of all parameters every 7.5s.