HART to a NON-HART communication

aec

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Sep 2011
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Hi all,
How to connect a FLOW transmitter which supports HART to a PLC which does not support HART ???šŸ“š
Details about products used:
PLC Delta DVP-28SV.(with digital and analogue I/o ā€˜s )
ABB Flow transmitter
At first the customer informed us it will be 4-20mA signal from the flow transmitter now he says it is HART.
From the PLC specification and catalog I could not find any module for HART communication.
Since this is my first experience with HART browsed the internet and learnt that it has both digital and analogue signal transmission through same wire.
I am looking forward for your suggestion and advice on how to proceed with this??????
How to get the signal flow transmitter to my PLC ???????:confused:
Have attached details about flow Transmitter and PLC for more details
Thank you .:site:
Details about PLC see the below link .http://www.delta.com.tw/product/em/control/plc/download/manual/DVP-28SV_instruction_en.pdf

flow transmitter Page 1.jpg flow transmitter Page 2.jpg
 
I'm not familiar with your PLC, but it doesn't look like it has much by the way of communications options...

If it supports MODBUS you could purchase a HART Gateway (such as this one - http://www.prosoft-technology.com/content/view/full/7156) to communicate with the flowmeter.

But to be honest, it's just a flowmeter. In 99% of applications, all you need is the 4-20mA for the instantaneous flow, and maybe the pulse output for a totalizer (connected to a normal digital input or a high speed counter).

What's the application?
 
I'm not familiar with your PLC, but it doesn't look like it has much by the way of communications options...

If it supports MODBUS you could purchase a HART Gateway (such as this one - http://www.prosoft-technology.com/content/view/full/7156) to communicate with the flowmeter.

But to be honest, it's just a flowmeter. In 99% of applications, all you need is the 4-20mA for the instantaneous flow, and maybe the pulse output for a totalizer (connected to a normal digital input or a high speed counter).

What's the application?

Hi saffa,

Thanks for your immediate reply (y).
If I connect the 4-20mA straight to my analogue input of plc will it work ?????? because it has been mentioned like
Current output (4 to 20mA)-HART (FEX100) Variant for the flow meter ?

My application is to get "current flow" and "total flow" .

This PLC supports modbus ascii/rtu through rs485 .

I would prefer it to be normal 4-20 mA so that it will be connected to the analogue input module for programming .
 
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+1
But to be honest, it's just a flowmeter. In 99% of applications, all you need is the 4-20mA for the instantaneous flow, and maybe the pulse output for a totalizer (connected to a normal digital input or a high speed counter).
 
Generally,

The Totalizer should be read as a floating point variable through your communication option purchased with the Flowmeter,

For example, if the Flowmeter was purchased with HART, then the totalizer and analog values would be read through the same 4-20mA loop, the Totalizer through reading an address, and the instantaneous through the 4-20mA cct.

If however you purchased a HART enabled Flowmeter, chances are that MODBUS is not available as well on the same Flowmeter. (That means that you are SOL of reading the totalizer through comms) (Most do not co-exist, it is either one or the other)

We use HART for some devices, but Modbus is more common, and is simple to use.

Either way, the Instantaneous can be read through your 4-20mA loop regardless.

Integration calculations don't work well, depending on your situation....
 
Because the Hart signal is a high frequency communications signal superimposed on the 4-20 mA signal it is filtered out of almost all 4-20 mA devices, including PLC inputs. The PLC won't know the Hart signal is there and your loop will work fine. I've done this many times, where the Hart is specified in the device "shelf" spec but nobody on the application end really knows what it means. We often use the Hart just for troubleshooting with a hand held, and use the 4-20 mA for PLC input and process control.
 
Because the Hart signal is a high frequency communications signal superimposed on the 4-20 mA signal it is filtered out of almost all 4-20 mA devices, including PLC inputs. The PLC won't know the Hart signal is there and your loop will work fine. I've done this many times, where the Hart is specified in the device "shelf" spec but nobody on the application end really knows what it means. We often use the Hart just for troubleshooting with a hand held, and use the 4-20 mA for PLC input and process control.

Exactly as Tom has stated r.e. the 4-20mA loop.

I just set up a Endress & Hauser FMU40 2-wire ultrasonic last week. I do all the configuration via HART (with the E&H commubox or whatever it's called) while the instrument is still producing a 4-20mA signal. It's handy for configuration but a bit clumsy as a fieldbus, and very few control systems (that I've come across at least) read HART directly - hence the need for some sort of HART-to-Something Else Gateway.

So go ahead, just use the 4-20mA as usual.
 
1) If your customer uses HART for any reason, for instance, to troubleshoot or to check calibration, then the loop should include at least 250 ohms of resistance so that HART communications can take place.

Many analog inputs use 250 ohms as the value of the resistor that converts the DC current to a DC voltage for further use on AI card. But if your customer's PLC does not use at least 250 ohms for its AI input resistance, then adding enough resistance somewhere in the loop [not across the AI (+) and (-), somewhere else] would allow the customer to use HART without having to break the loop and add a resistor to get HART working.

Adding enough resistance to facilitate HART communications will not affect the 4-20mA signal.

2) There are very few PLCs that offer high end AI cards that can handle HART, and the only 3rd party supplier that I've heard of makes an A-B compatible card.

3) The Siemens flow meter I was working with last week had both a 4-20mA for instantaneous flow rate and a (relatively) low speed pulse output that could be configured for X flow volume per pulse. Have you checked for a pulse input that you can run to a DI and count for a total, like Bob O recommends?

4) I agree with SNK that Modbus and HART never co-exist on the same device.
 
Thank you all for your time and response(y):site:

I am happy that I can use 4-20mA but still I will confirm this with my boss and the customer.

The totalizer calculation or the total flow is what I am concerned about now beacuse it will not be accurate :confused:.

This flow transmitter also supports profibus and also it trasmits frequency output to the PLC .

is this frequency output from the flow transmitter is concidered as pulse input to the PLC šŸ“š?????????
Sorry if the question is too dumb but I am learning so please kindly bear with me :confused:šŸ“š

Thank you all for your time and response I am happy that I am learning (y)(y).:site::site:
 
The totalizer calculation or the total flow is what I am concerned about now beacuse it will not be accurate :confused:.

It really depends on what you are trying to do. If you just need daily, weekly or monthly totals then you should experience no loss of accuracy. The only time you're going to "lose" pulses is if someone powers down your PLC, downloads a program and doesn't save data values first, or disconnects the pulse wire.

If you need to display EXACTLY what's shown on the meter's internal totalizer then reading that totalizer via a digital comms bus is the way to go.

I use the pulse outputs from ABB flowmeters all the time for daily, weekly and monthly totals just with a normal digital input. Just make sure that the pulse width set in the flowmeter is long enough that your PLC will "see" a transition within 1 scan time. If you set it to 1000ms that should be plenty safe, provided the actual flowrate being put through the meter would not result in pulses more often than every 2000ms.

Do you know the expected maximum flowrate for your application?
 
Hi safa ,
Many thanks for ur response(y)

It really depends on what you are trying to do. If you just need daily, weekly or monthly totals then you should experience no loss of accuracy. The only time you're going to "lose" pulses is if someone powers down your PLC, downloads a program and doesn't save data values first, or disconnects the pulse wire.

If you need to display EXACTLY what's shown on the meter's internal totalizer then reading that totalizer via a digital comms bus is the way to go.


I donā€™t know whether the customer need exact or daily weekly or monthly I will get the information and update here

If I want to read exactly whatā€™s shown on the meter ā€“ then what is ā€ digital comms ā€œdo you mean through HART communication ????

I use the pulse outputs from ABB flowmeters all the time for daily, weekly and monthly totals just with a normal digital input. Just make sure that the pulse width set in the flowmeter is long enough that your PLC will "see" a transition within 1 scan time. If you set it to 1000ms that should be plenty safe, provided the actual flowrate being put through the meter would not result in pulses more often than every 2000ms.

  • ABB flow meter is it same as what I am using??????
  • Sorry which output is pulse output and from which normal digital input????
  • Pulse width ??????
  • Could you please tell me how you wired from the flow transmitter to the PLC?????? PleasešŸ“š
Do you know the expected maximum flowrate for your application?



No , I will ask . what else should I have to consider.


Adding some information , after reading your post I made some search and found that the PLC supports 2-group (y0,y1)(y2,y3)A,B phase pulse output,with 200 kHz. and also 2-point (y4,y6)high speed pulse output with 200 kHz.
but there is no pulse input point .


The flow meter has
Pulse Output 1 / Logic Output 1 and Pulse Output 2 / Logic Output 2 (terminal 41 and 51)

What is pulse is it similar to digital or a seperate programming is required????

How should the wiring be connected ?????
Thanks a TON :site:
 
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>The flow meter has Pulse Output 1 / Logic Output 1 and Pulse Output 2 / Logic Output 2 (terminal 41 and 51)
What is pulse is it similar to digital or a seperate programming is required????

Answer: There's probably 8,000 flow meters on the market today. There is no single answer to your question. You have to open the manual for the particular device and read what a pulse output does.

For example:
On a Siemens magmeter, the pulse output changes state every X volume units. When wired to a PLC digital input, the pulses are counted and scaled with a resulting total value.

On a Siemens Clamp-on ultrasonic flowmeter, the pulse output does not pulse for volume output like the magmeter, the pulse output is signaling bidirectional flow, alarms and status events.

Two Siemens flowmeters, two entirely different approaches to what a pulse output does.

The clamp-on does have a frequency output which is a flow rate output, not a total output.

For a span of 0 to 100L per minute,

At 100L/min, the output is an instantaneous 5.0Kz.
At 50L/min, the output is 2.5KHz
At 25L/min, the output is 1.25KHz

If the totalizer's time base is accurate and the sampling is consistent and frequent enough, totalizing an analog value can have surprisingly good accuracy. I totaled an analog value on a paperless recorder and comparing it to the pulse total, it had only 0.3% error over 4 hours.
http://blog.lesman.com/2012/04/18/f...pulse-input-totalizer-comparison/#more-638And
and that was without a calibration on the AI, which could likely further reduce the error.
 
hi Aec,

From the 2 pages of the manual you posted in your original post, you have an ABB WaterMaster.

By "Digital Comms" I mean reading from the meter via a HART Gateway of some kind. Lets not go down that route for now, since I think it'll likely be overly complicated and since I'm not familiar with your PLC's communications options I wouldn't be much help if you got stuck.

If you look in the WaterMaster manual, they describe in Section 4.6.1, Frequency Outputs. these are the pulse outputs I was talking about, and can be connected to a normal, digital input on your PLC. These are open-collector transistor outputs on the flowmeter, and should be connected as "Sink" inputs as shown on the PLC brief manual you posted in your first post.

That is, connect from +24V to terminal S/S, then from the flowmeter terminal labelled O/P1 to X0 (assuming you were using input 1 as the pulse input), then from the flowmeter COM terminal to 24V Ground.

Now if you power up the flowmeter, you should be able to go to the Inputs / Outputs menu and set the function of O/P1 and the pulse width. Check the programming manual for the WaterMaster, available on the ABB website if you don't have it - http://www05.abb.com/global/scot/scot203.nsf/veritydisplay/347fc15fe40b34dcc12577ec004a52f5/$file/IM_WMP_E.pdf

Pulse output config is described on page 22-23 (PDF reader page 24-25). I'll let you have a go at figuring this out, it's not hard. Basically you need to set the function to forward Pulse, set the units (m3, litres, gallons, whatever) and then the pulse width.

If you put the meter into simulation mode (via diagnostics menu), you can dial in a simulated flowrate and the pulse output will trigger accordingly. You can use this to test your program.

Now all you need to do is write your PLC program to count positive transitions of the input X0 and voila, you're counting whatever flow unit you configured the flowmeter for!
 
Thank you all ,

Now I am getting an idea as how it works .Thank you danw and Saffa (y).At present there is no power in the site.

Once when it is ready I will try what you have told and update here about what happenned .

Now I have got some idea really that was a good explanation thank you very much (y).Now I am some what confident because I now know where to start . Eager to check how it works:book: .

:site::site:
 

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