victorbrave
Member
Can you post a drawing!!!....please!!!...
How to build a 4-20 mA source for testing?
- Thread starter klittle
- Start date
Can you post a drawing!!!....please!!!...
victorbrave
Member
How you do it?...drawing please!...
Mickey
Lifetime Supporting Member
victorbrave
Member
Thanks!...
nonuke
Member
- Join Date
- Sep 2005
- Posts
- 840
I know it's an old post, but need help.
I built MikeVT 4-20 mA source for testing purpose, and it
works OK if I use a milliamp meter at the output to read the mA value.
I would like to install a digital panel meter powered by the current loop instead of using the milliamp meter. The problem is that at lower mA values the voltage drops and I will not be able to read the value in the meter.
Is there a solution for this?
I built MikeVT 4-20 mA source for testing purpose, and it
works OK if I use a milliamp meter at the output to read the mA value.
I would like to install a digital panel meter powered by the current loop instead of using the milliamp meter. The problem is that at lower mA values the voltage drops and I will not be able to read the value in the meter.
Is there a solution for this?
danw
Lifetime Supporting Member
I'm curious. What do you use the ramp function for?
Watching alarms trip?
How slow should it ramp between 2 points to be useful?
5 seconds across 5% of span?
Current simulator
This is very interesting and cheap.
Could you post how to place the jumpers to simulate powered or self powered transmitter?
Thank you,
MifPT
This is very interesting and cheap.
Could you post how to place the jumpers to simulate powered or self powered transmitter?
Thank you,
MifPT
holyhobgoblin
Member
Howdy Folks
New to the forum and just need a helping hand.
I built the 4-20ma simulator last week that MikeVT post at the beginning of the thread. Used it the next day and it really saved my bacon as I need to confirm that 4 x Temp Controllers using 0-10v inputs were working correctly. I noticed whilst using it the outputs were 4.67-32ma and 0-18v, now I used 2 x 1N4007 for the diodes and a LM317LZ instead of the LM317 or LM317L, tested the 10k pot that was fine, it was connected to a 24vdc source.
Would this be because I used a LM317LZ or simply cheap nasty resistors?
Also has anyone come across cheap RTD & Thermocouple simulators? or even know how to build one. I deal with a lot of Temperature and process controllers and would be a helpful tool.
Thanx in advance for the help.
New to the forum and just need a helping hand.
I built the 4-20ma simulator last week that MikeVT post at the beginning of the thread. Used it the next day and it really saved my bacon as I need to confirm that 4 x Temp Controllers using 0-10v inputs were working correctly. I noticed whilst using it the outputs were 4.67-32ma and 0-18v, now I used 2 x 1N4007 for the diodes and a LM317LZ instead of the LM317 or LM317L, tested the 10k pot that was fine, it was connected to a 24vdc source.
Would this be because I used a LM317LZ or simply cheap nasty resistors?
Also has anyone come across cheap RTD & Thermocouple simulators? or even know how to build one. I deal with a lot of Temperature and process controllers and would be a helpful tool.
Thanx in advance for the help.
jdbrandt
Lifetime Supporting Member
Roy Matson
Member
I don't see the circuit you mention.
You may need to be able to trim the resistors to get the right current.
I have a calibrator design based on the 317 regulator, it also allows me to do RTDs and simulate thermocouple inputs using the tables.
Roy
You may need to be able to trim the resistors to get the right current.
I have a calibrator design based on the 317 regulator, it also allows me to do RTDs and simulate thermocouple inputs using the tables.
Roy
John Soltesz
Member
Yea, there are loop powered process meters like Red Lion CUB4LP (http://www.redlion.net/Products/DigitalandAnalog/DigitalPanelMeters/Process/CUB4LP.html)
Just scale it for 4-20. Now when you get somewhere below 4ma the meter won't have enough power to scavenge off of.
I think this is what you want but if you want to read toward 0ma then a powered meter is the only way. OR get a mechanical meter.
Last edited:
holy guy
your problem is with the resistors, make one a little different so you can use it even lower the 32 is a little high (some machines can not cope above 25 mA.
Use a variable resistor (potmeter to find both setting and then solder the value with a fixed one in.
An RTD simulator is very easy to build by using some resistors and a turnswitch.
best is to use a four deck switch and soler the resistors direct on the switch.
A thermocouple can be build with the voltagemaker and some resitors
your problem is with the resistors, make one a little different so you can use it even lower the 32 is a little high (some machines can not cope above 25 mA.
Use a variable resistor (potmeter to find both setting and then solder the value with a fixed one in.
An RTD simulator is very easy to build by using some resistors and a turnswitch.
best is to use a four deck switch and soler the resistors direct on the switch.
A thermocouple can be build with the voltagemaker and some resitors
Roy Matson
Member
Loop Calibrator
Here is a simpler version of mine without the milivolt source.
If you look at the upper diagram it shows how it works.
The lower diagram shows the actual circuit.
The nice thing about this it both sources and simulates, it doesn't even need a battery to simulate.
A page or so back I show the full blown version with thermocouple / RTD simulation (millivolt / resistance)
I made mine over 30 years ago, in that time i have replaced a couple of switches and many batteries but it's never needed re-calibration.
Roy
Here is a simpler version of mine without the milivolt source.
If you look at the upper diagram it shows how it works.
The lower diagram shows the actual circuit.
The nice thing about this it both sources and simulates, it doesn't even need a battery to simulate.
A page or so back I show the full blown version with thermocouple / RTD simulation (millivolt / resistance)
I made mine over 30 years ago, in that time i have replaced a couple of switches and many batteries but it's never needed re-calibration.
Roy
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