×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Vortex Flowmeter

Vortex Flowmeter

Vortex Flowmeter

(OP)
Hi!!

Can anyone help me on this question.  I am looking at a vortex flowmeter and the transmitter load line resistance is given as max 550 ohm at 24V?  Does this mean the signal output from the transmitter can drive a max load of 550 ohm at 24V or 43.6mA?  How is this important when I source for a digital controller?  What parameter in the digital controller needs this piece of information? Thank you!!

RE: Vortex Flowmeter

A 24Vdc power supply in series in the output loop will drive up to 550 ohms of loop resistance.

A lower voltage does not necessarily limit the output current ability, but it does lower the maximum load resistance possible in the loop.

The manual for the flow meter undoubtably contains a chart similar to the one below that shows how much loop resistance any given power supply voltage will drive.



The practical implications are that any analog input on a DCS/PLC/controller/recorder/whatever develops a voltage drop when the 4-20mA current runs through the input resistor.

Many systems use 250 ohms for an input resistor.    Yesterday, I discovered Automation Direct uses 125 ohms.  I've seen other values used: 1 ohm, 10 ohm, 62.5 ohms and 500 ohms.

The point being that the available voltage has to support the total load resistance.  

If you are supplying the flow signal to only one device it is (almost) a given that it will be OK.  If you run the flow signal in series to 2 or more devices, you have to add up the load resistances of each and if the wiring is a really long run, take the copper resistance into account too.  

For instance, two, 250 ohm loads and 7.6 ohms of wire add up to 508 ohms, which would be less than 550 ohms that a standard 24Vdc power supply could drive.

Dan

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources