displaying a pulsed output of a flowmeter

learningPLC

Member
Join Date
Apr 2015
Location
tunisia
Posts
6
Hi All,

I need your help in this task

I have to read (visualise) the output of a flowmeter in kg/s on an HMI screen (before I use it in a flow control loop to adjust a valve).
The problem is it's a pulse output so I'm a little bit confused since I've been always working with analog sensors output (0-10V/4-20mA...) using SCALE/UNSCALE

Do I need to use a counter for pulses ?
What I/O module to use in HW config ?

I am using Siemens Step 7 v5.5
315 CPU

Thank you.
 
Thank you for replying

It's about 15 pulses/s

The problem is that all still theoratical (a preliminary study), and still don't have the floweter I only know that it has a pulsed output, with a range about 0-5kg/s
 
You should not have a problem with a standard digital input card from Siemens with a period of 67ms. You probably have to program the ON/OFF time of the flowmeter pulses so the ON and OFF time are about the same (33 ms)
 
Ok, so If I understand you well

I need the digital input card connected to the flowmeter and the PLC to manipulate the pulsed output.

My problem is I don't know how to convert the pulse output I have into kg/s to display it on HMI screen .

Should I use a certain counting function for example to count pulses in a certain duration (xx pulses/min or xx pulses/s) then use "SCALE" to convert it to a flow rate (kg/s) ?
 
Yes you can do that, but the flowmeter also has an analog output for the flow. this is the reason why it is called a flowmeter.
The pulse output from the flowmeter gives you the amount of liters total, partial etc.

If you don´t have the analog output from the meter, then you must do what you wrote in the previous post.
 
Last edited:
two ways to check for speed:
count the pulses in a certain time, or count the time for a certain number of pulses.
The speed of pulses is the factor here. So you will need a high speed counter card (67ms is way to slow). and check every second how many pulses are in the counter subtract this number from the counter and go on.
 
thanks for helping,
I'm trying to use a digital input module since the speed of pulses have chaged to 10 pulses/s max now, with an SFB47 as a counter .

Is that possible ?
 
What exact model CPU do you have? Many of the C-CPU's have built in HS counters. I would not use a standard input.

Reading your comments, it seems like you are in over your head. A great way to learn if you have the time, if not, I would go with a converter as Osmanmom says.

Regarding conversion from pulse to flow, I would measure the time over a certain amount of pulses. In your application I would pick 15-20, this should make it more accurate.
 
You also need to consider the duration of the pulses from the meter. If you use a standard input and if the pulses are shorter than the scan time of the CPU, then it's likely that you'll miss a few and end up mis-calculating the flow rate.
 
The 314C has integrated pulse counter.

See chapter 5 in this document.

Read through it carefully, it is not the easiest thing to get running as a beginner, but I managed to do it, so it can't be that hard ;).
 

Similar Topics

Hello Folks, plc : micrologix 1500 The analog output from the loadcell is given to the plc. Using the SCP function I have scaled it into an...
Replies
3
Views
708
Hi Everyone, I am hoping a Red Lion Expert can point me in the right direction. I am experimenting with data logging on a CR3000 10" screen...
Replies
4
Views
556
I’m a bit stuck on HMI (KTP-1200) programming… See the picture attached. The PASS or FAIL box should only appear when the toggle switch is...
Replies
7
Views
972
I have 6 Red Lion DSP units displaying PLC strings and data to 6 industrial LED screens. After sending the .cd3 file from screen 2 to screen 6...
Replies
3
Views
993
Customer upgraded a Panel View Plus 7 Pro from the 10" to 12". I upgraded the project in View ME and downloaded to the HMI. Everything looks...
Replies
5
Views
2,227
Back
Top Bottom