All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > General Electronics Chat

Notices

General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

Reply   Post New Thread
 
Thread Tools Display Modes
  #21  
Old 09-30-2008, 02:45 AM
Ron H's Avatar
Ron H Ron H is offline
E-book Developer
 
Join Date: Apr 2005
Location: Idaho, USA (GMT-7)
Posts: 7,050
Default

If your PLC can measure pulse amplitudes, you can save a lot of heat and power by pulsing the current source. I am unfamiliar with PLCs, so I have no idea whether this is possible.
Reply With Quote
  #22  
Old 09-30-2008, 04:31 PM
viju viju is offline
Senior Member
 
Join Date: Sep 2008
Location: India
Posts: 111
Send a message via Yahoo to viju Send a message via Skype™ to viju
Default

Yes I can control my measuring time in milliseconds through PLC.If so, will I be able to measure the resistance?
Reply With Quote
  #23  
Old 09-30-2008, 09:30 PM
Ron H's Avatar
Ron H Ron H is offline
E-book Developer
 
Join Date: Apr 2005
Location: Idaho, USA (GMT-7)
Posts: 7,050
Default

Quote:
Originally Posted by viju View Post
Yes I can control my measuring time in milliseconds through PLC.If so, will I be able to measure the resistance?
To measure pulse amplitude, the PLC has to know when the pulse is present, so it can sample it. Is that something it can do?
If you can read voltage, the conversion to ohms is simple.
Reply With Quote
  #24  
Old 10-01-2008, 12:47 AM
viju viju is offline
Senior Member
 
Join Date: Sep 2008
Location: India
Posts: 111
Send a message via Yahoo to viju Send a message via Skype™ to viju
Default

Yes.You are right.I will design the fixture with a pneumatic pin plunged into the measuring point with source.After plunging the pins I will switch the source to ON.Through the sense pins I will read the voltage( well inside the source pins) and amplify it.I am right.
Reply With Quote
  #25  
Old 10-01-2008, 02:17 AM
Ron H's Avatar
Ron H Ron H is offline
E-book Developer
 
Join Date: Apr 2005
Location: Idaho, USA (GMT-7)
Posts: 7,050
Default

Quote:
Originally Posted by viju View Post
Yes.You are right.I will design the fixture with a pneumatic pin plunged into the measuring point with source.After plunging the pins I will switch the source to ON.Through the sense pins I will read the voltage( well inside the source pins) and amplify it.I am right.
That sounds good. Measure the voltage as close to the weld as possible.
Reply With Quote
  #26  
Old 10-02-2008, 01:50 AM
viju viju is offline
Senior Member
 
Join Date: Sep 2008
Location: India
Posts: 111
Send a message via Yahoo to viju Send a message via Skype™ to viju
Default

Hi Bill,

Awaiting your transistor based constant current circuit.

Wookie and Steve:

I have just built the circuit and tested it.It works fine but with some heat in the regulator IC. I have a SMPS meanwell ( 24V,2.1amps) connected to 7805 regulator IC which feeds to LM 317.And to remind you I am building this for a automated production line where the cycle time for checking the subject is of less than 2 seconds.Our company works 16 hours a day.SO assume how many times the measurements are made.Please help me.
Reply With Quote
  #27  
Old 10-02-2008, 01:53 AM
hgmjr's Avatar
hgmjr hgmjr is offline
Super Moderator
 
Join Date: Jan 2005
Location: Tennessee, USA (GMT-6)
Posts: 9,030
Blog Entries: 11
Default

One way to reduce the dissipation in the 7805 is to lower the voltage at its input. If you drop it to 10 volts, that will cut down significantly on the wasted power that is heating the 7805.

hgmjr
Reply With Quote
  #28  
Old 10-02-2008, 02:58 PM
Ron H's Avatar
Ron H Ron H is offline
E-book Developer
 
Join Date: Apr 2005
Location: Idaho, USA (GMT-7)
Posts: 7,050
Default

You said your cycle time is less than 2 seconds. What is the minimum pulse width that will still allow you to measure the voltage? If it is short relative to ≈2 seconds, then the duty cycle can be low, minimizing average power.
Reply With Quote
  #29  
Old 10-02-2008, 06:16 PM
Bernard's Avatar
Bernard Bernard is online now
Senior Member
 
Join Date: Aug 2008
Location: Tucson AZ USA
Posts: 2,971
Default

Why not just use a 24Ω 10 W resistor and 12 V in series with work piece ??
Reply With Quote
  #30  
Old 10-03-2008, 04:04 AM
Bill_Marsden's Avatar
Bill_Marsden Bill_Marsden is offline
Super Moderator
 
Join Date: Mar 2008
Location: Dallas, TX (GMT-5 w/ DST)
Posts: 18,802
Blog Entries: 5
Default

A constant current source has some interesting properties. Basically you are making an ohm meter (a calibrated one). If you try to use a fixed resistance then the resistance in the device under measurement (in this case the pipe) significantly affects the results, with a constant current source it doesn't.
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
Reply With Quote
Reply   Post New Thread

Tags
, ,


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help with Opamp/PNP Transistor Current Source sohcahtoa The Projects Forum 9 08-26-2009 03:36 PM
constant current source unlv007 General Electronics Chat 42 04-25-2008 10:49 PM
Constant Current Source, Current Mirror?? robby991 General Electronics Chat 13 01-26-2008 06:40 PM
About Thevenin Theorem BrillianceLin Homework Help 3 12-04-2007 05:42 PM
capacitor across a constant current source sinlikenkuri General Electronics Chat 2 07-31-2006 05:41 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 06:37 PM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.