1734-IB8 digital input frequency reachable

I need to set the frequency of a pulse output that will be read like a direct input in a 1734-IB8. So, I read the module especifications but I didn't find about the minimum frequency that can be detected by the input. Can you help me?

minimum frequency? 0 - Hz (DC)

Let's presume OP meant maximum frequency, or meant minimum pulse duration.

In general a POINT I/O DC input module has a 0.5 millisecond input delay plus a 0-63 millisecond user-configurable input filter.

The issue is that these modules are scanned by a network adapter or the backplane scanner of a CompactLogix, so the bigger question is the speed at which the controller and network can update the module. There are multiple variables and no easy answer without more information from the OP about the network.

Ordinary 1734-IB8 modules are not appropriate for counting or pulse input applications. Use the 1734-IJ, -IK, or VHSC modules for encoder applications.

Yes, maximum frequency/minimum pulse duration.

If we take that 0.5ms Off-to-On delay and assume no input filtering time.

0.5ms = 2000Hz maximum frequency just for Off-to-On.

If we assume 2000Hz also for On-to-Off, this is now 4000Hz or 4kHz.
This is the fastest frequency the pulses can input to the module.
Not very fast really. But you should never input to a modules maximum.
You should allow headroom.
So that 4000Hz could have to be lowered a bit to avoid dropping pulses.

Every 1ms you add in filter time deducts 1000Hz off your maximum frequency.
If you have a 200,000Hz (2kHz) input, then that is not so much, but to a 4kHz input it is a lot.

And that's all before the backplane/adapter/port/wire/port/backplane/processor delays are included as Ken mentioned.

Your question is a bit inverted really. You seem to want to set the pulse rate to the input hardware rate, when normally you need to spec the input hardware to capture the required pulse rate?

Regards,
George

Yes, maximum frequency/minimum pulse duration.
Ok, Thank you for helping. Actually my hardware configuration is a CLP 1769-L33ER (Compact Logix) connected through ethernet network to a 1734-AENT/A that have some 1734-IB8/C in his rack. So, I have to configure the frequency of a pulse that is send to an digital input by a flowmeter (in flowmeter manual they say that this pulse can be wired like a direct input). I just want use a frequency that can be monitored without problems.

(Correction: 200,000Hz = 200kHz, not 2kHz)

Can you provide the make/model number of the flowmeter?

Specifically, what is its maximum output frequency (Hz) when the maximum flow rate (E.g. GPM/LPM) is attained?

An ordinary discrete input module like the 1734-IB8 wired to an Ethernet adapter is not appropriate for a flowmeter input.

Use a high-speed encoder/counter moudule with an appropriate voltage rating instead: 1734-IJ (for 5V DC) or 1734-IK (for 24V DC).


The 1734-IJ or -IK modules have a maximum input frequency of 1 MHz and have built-in Rate measurement modes.

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.

the flowmeter model is 8800D Vortex Flowmeter by Emerson
Optional scalable pulse output
0 to 10000 Hz

"0 to 10000 Hz"

10kHz...Forget it!

Even half that flow rate is way too much for the 1734-IB8.

Your looking at a speciality module like the -IJ or -IK as Ken suggested.

G.