Rockwell Automation 1771-CFM,D17716.5.99 CONFIGURABLE FLOWMET - Manual (Page 47)

4–13 Configure the CFM Module
Publication 1771Ć6.5.99 - December 1995
Use these diagrams to understand how you use Sampling
Termination and Bandwidth Limit to exert even more control over
the CFM module’s frequency sampling.
The CFM module calculates
frequency on the next pulse
to occur after time expires. 1
Sampling Termination
(word 5, bit 13)
set (ON)?
Sampling Termination
(for input channel 0)
Y
N
CFM module calculates
frequency based on Minimum
Frequency Sampling Time
(word 6) ➀
➀ The module calculates a new frequency on the next pulse to occur after the
expiration of the specified time; therefore, the actual period will be longer than
specified in word 6. Upon calculation of the frequency, the outputs are updated.
Minimum Frequency
Sampling Time
(word 6)
expired?
N
Number of Pulses
to Terminate Sampling
(word 7)
received?
Y
N
Y
CFM module calculates
frequency immediately after
the specified number of
pulses occur.
Bandwidth Limit
(word 5, bit 14)
set (ON)?
Bandwidth Limit
(for input channel 0)
N
The CFM module can distinguish frequencies as low as 1Hz.
At low frequencies (< Minimum Frequency Sampling Time),
the CFM module may take as long as 2s to calculate a new
frequency value.
The minimum frequency the CFM module can detect
is 1/Minimum Frequency Calculation Time.
When set, the CFM module will spend no more than
(2 x Minimum Frequency Sampling Time) to
determine a new frequency value.
Y
Terminate Conditions ➀
Sampling
termination
Bandwidth
limit
Minimum frequency distinguishable Frequency sample taken ➁ and outputs updated when
OFF (= 0) OFF (= 0) 1Hz
Minimum Frequency Sampling Time elapsed
and at least one pulse received
OR
2s elapsed and no pulse received
OFF (= 0) ON (= 1) 1/Minimum Frequency Calculation Time
Minimum Frequency Sampling Time elapsed
and at least one pulse received
OR
(2 x Minimum Frequency Sampling Time) elapsed
and no pulse received
ON (= 1) OFF (= 0) 1Hz
Number of Pulses to Terminate Sampling received
OR
Minimum Frequency Sampling Time elapsed
and at least one pulse received
OR
2s elapsed and no pulse received
ON (= 1) ON (= 1) 1/Minimum Frequency Calculation Time
Number of Pulses to Terminate Sampling received
OR
Minimum Frequency Sampling Time elapsed
and at least one pulse received
OR
(2 x Minimum Frequency Sampling Time) elapsed
and no pulse received
➀ The terminate conditions assume a start pulse has been received.
➁ The next sample begins at the first pulse that occurs after a valid sample is taken.