How do I convert Pulse Output from a flow sensor to RS485 / 4-20mA?

Question

How do I convert Pulse Output from a flow sensor to RS485 / 4-20mA?

kdv1988 (Mechanical)

(OP)

5 Feb 23 05:21

Hello,

Thinking of building a pilot project for one of my customers wherein I install simple flow sensors on multiple machines and connect their outputs to an IIOT gateway. Now the issue is that because of budget restrictions, I can only afford very basic flow sensors meant for water (the hall effect ones) which give a Pulse Output. And the Gateway can only accept inputs in RS485 or 4-20mA.

How do I do this conversion? Will it cost a bomb? Because if a 'converter' is required per flow sensor, I may have to get many of those as there could be as many as 50 flow sensors required for this client.

IRstuff (Aerospace) · Answer 1 · 2023-02-05 05:33:22

Like this? https://www.abestmeter.com/hall-effect-flow-sensor....

If so, then yes, you will need a converter for each one; what makes you think otherwise?

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kdv1988 (Mechanical) · Answer 2 · 2023-02-05 06:52:45

Figured I might need one for each sensor. What I meant to ask was what would be the economical way to do it?

3DDave (Aerospace) · Answer 3 · 2023-02-05 15:37:07

It depends on why all of this monitoring is happening.

Worst case:
All points need to be continuously monitored for precision totalizing of flow and control of instantaneous rate.

Best case:
A few process points need confirmation fluid is flowing, most are idle.

In the worst case, it should be cheaper to have integrated electronics with the meters programmed with flow requirements and control valves directly with polling to provide an overview and accept meter generated alarms.

In the best case, it might be possible to use analog multiplexers to allow selection of a limited number of meters which would be cheaper than the first case.

It may not be so large a difference given that installation and wiring will be a significant cost as will the cost of on-going maintenance and the initial software development. Double the cost for sensors might be a 10% increase in cost for the system, but in exchange one gets far better information.

Answer 4

[Post Deleted]

TugboatEng (Marine/Ocean) · Answer 5 · 2023-02-05 20:24:53

You're looking for a RS485 counter module. After a quick Google only I only see them with up to two channels. However, if you have a computer on this network you should be able to use a digital input module and simply count the pulses with your data acquisition software.

Compositepro (Chemical) · Answer 6 · 2023-02-06 02:37:23

Many speed sensors are pulse-output and there are transducers to change this to other outputs. To keep cost down, you would need a multiplexer to switch the pulse train from the sensors to one transducer. You can count pulses per unit time for high pulse rates, or the period between pulses for low pulse rates. And a data acquisition system to keep track of the data.

danw2 (Industrial) · Answer 7 · 2023-02-06 18:09:59

The flow meter output is a pulse frequency proportional to flow; x pulses per second represents Y flow per sec/min/hr. Whatever receives the pulses needs hardware and enough logic to convert the incoming pulse stream to volumetric flow units per second/minute/hour, whatever the case may be.

The gateway should not be passing pulses, it should be passing data values. Is the total needed, too?

There's a device that concentrates a lot of flow pulse inputs into one box - the Precision Digital Consolidator. It has 7 slots, each slot can take a four channel pulse input card for a total of 28 pulse inputs. It includes an HMI screen which can display the digital flow rate values and can totalize each channel as well. It configures through menu selection, not PLC style blank slate programming.

Modbus RTU over RS-485 is standard. Modbus over Ethernet is an option, and, warning its implementation is unique, requiring configuration using the OEM Ethernet module's (Lantronix) DeviceInstaller software.

But it's one box that does a whole lot in terms of consolidating the conversion to flow rate task and making the flow rates (and totals?) available via Modbus.

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How do I convert Pulse Output from a flow sensor to RS485 / 4-20mA?