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!

*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.

Jobs

How to calculate maximum error?

How to calculate maximum error?

(OP)
Hi,
I am wondering how I can calculate the maximum error of a measurement chain.
If I have a voltage transducer with a accuracy of +-1%, which is wired to analogue input of a PLC (12 bit), what's the error of it?
The output of the transducer is 0-10V so as the input.

Cheers,

Lars

RE: How to calculate maximum error?

Not easy to say. You haven't said anything about the error of the PLC input. All we have to go on is the resolution, which is 12 bit. We do no know if it is unipolar (12 bits across -10 V to +10 V) or bipolar (12 bits across 0 to 10 V). In the former case, you will have around 0.05% and in the latter case 0.025% of range resolution.

The general rule to add independent errors is RMS and that means error is sqrt(0.01^2 + 0.0005^2) or 0.01001, which corresponds to 0,01001 or 1.001% error, which means that you can forget about the influence from PLC resolution.

So, it is very important if your transducer's error is ten times or more. On the other hand, if your PLC isn't better calibrated than 1%, then your RMS error will be sqrt(1^2 + 1^2) or 1.4%. The maximimum possible error will be 1 + 1 = 2%

Then you have to decide if this is linearity only or offset plus linearity. And, then again, is your error refered to range, maximum value or actual value?

It is almost impossible to state what the error is without going into lots of details like that.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: How to calculate maximum error?

Just remember the rules of digital sampling. I think if you want 1% accurancy your sampling has to be 2x that accurate. That includes your sensor, how you configure that card in the plc (RPI), the task that its called from has a scan time. Just something to think about.

RE: How to calculate maximum error?

That is more about Nyquist, isn't it? Not so much about calibration, non-linearities and offsets.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close