Ken,
In general I would agree, but there are certain pulse flowmeters with relatively low output frequencies, even at their maximum flow rate.
An example...
Flowmeter which ranges from 0.06 to 60 GPM, 0.1 to 300 LPM
The output frequency is proportional to flow rate through the meter.
At the maximum flow rate the output frequency is approximately 240Hz.
At the minimum flow rate the frequency is approximately 10Hz.
The 1734-IB8, including potential communications latency, would handle this relatively easily, but wear and tare should be considered too.
That is why I would like to see the flowmeters maximum frequency.
Also, the maximum frequency could be too high, but they may only ever need to measure a small percentage of the flowmeters full range, depending on the process.
But I do agree that in general PWM, counter, or very high speed counter modules or inputs should be used. The counting is also done in the hardware asynchronous to the program scan. A lot more reliable.
G.