4-20ma sensor
Signals
Posts: 3
Hi from newbie
I want to adapt stamp projects to existing 4-20ma equipment. At first I will not be
able to "connect" to the circuits. I will need to sense the current via a clamp on
type of device. Any ideas or products that can clamped or wrapped around a wire that
is conducting a 4-20ma signal for use with the Basic Stamp?
TIA
I want to adapt stamp projects to existing 4-20ma equipment. At first I will not be
able to "connect" to the circuits. I will need to sense the current via a clamp on
type of device. Any ideas or products that can clamped or wrapped around a wire that
is conducting a 4-20ma signal for use with the Basic Stamp?
TIA
Comments
This might be something to looking into
http://www.fieldpiece.com/accessory-heads.html·· Almost at the bottom of the page
Measures milliamps and microamps for flame diode test. Measures 4 to 20mA control circuits.
Includes flame diode adapter kit (AQK3).
Resolution: 0.1 for meters with 0.1mVDC.
Accuracy:
DC: ±(1.0%rdg + 1dgt)
AC: ±(1.5% + 2dgts).
Max current: 200mA
AC or DC
. I do not know of any heads that are for meters that will work well enough for what you want to maybe some one on the forum may know of one
I hope this will help you
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··Thanks for any··that you may have and all of your time finding them
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Sam
Buy a precision 250 Ohm resistor .. 4-20MA thru this to GND converts it to 1-5V
Measure this with a A/D converter..
cheers
Ronald Nollet Australia
For monitoring continuous current, it's not too good. If you DID clamp on a device (or even wrap a coil of wire around another wire) that device would only get a signal when the 4 to 20 mA signal changed. I'm not sure that's good enough to reconstruct the signal -- but I could be mistaken about that.
I typed the above before I checked out that web site listed above
Post Edited (cyplesma) : 8/30/2007 6:30:28 PM GMT
I have too many dead brain cells (almost 60).
Have to figure out how to get the owner to let me add a pair of jumpers to the
chart recorder (driven by 4-20ma) and use voltage at the wire nuts for the Basic Stamp.
My next question
Would using a set of jumpers across the 4-20ma lines at the chart recorder change the values on the chart recorder? I am sure I would not be allowed to hook up if the values change or if I had to re-calibrate things.
I assume I will have to use a ADC chip and the current requirement will extremely low.
TIA
but I also think to help any further need to know what type of device your trying to tap signals from
Current loop systems maintain a given current for a given input (that's their calibration) but there is a limit on the driving voltage that forces the current (it will be maximum at 20 ma). This is one reason why current loops are used instead of voltage levels... you don't worry about line loss if the system can jack the voltage up to maintain the current through whatever the resistance of the lead wires is. The other reason is lower noise. However if you put in a large enough resistor to generate 5 volts across it at 20 ma, you're asking the system to boost its voltage by 5 volts to keep the current up and it's highly unlikely that the system will be able to do that.
Adding a small resistor shouldn't affect the calibration at all.. it's just like adding some lead wire. Be sure to use full differential amps and be careful not to introduce noise.
There are dc clamp on amp meters, but I don't know how they work
There are dc clamp but for a good one you hve spend a lot of money
and they are hard to find
Here you find one
·http://us.fluke.com/usen/products/category.htm?category=CLMP(FlukeProducts)&parent=CLMP(FlukeProducts)&PK=CLM&gclid=COmfroWcoI4CFSMOgQodkjwMTw
Here one more
http://www.extech.com/instrument/categories/clampon/subcategory/acdcClamp.html
http://www.multimeterwarehouse.com/clamp.htm
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··Thanks for any··that you may have and all of your time finding them
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Sam
Post Edited (sam_sam_sam) : 8/31/2007 5:13:11 PM GMT
http://www.api-usa.com/pdf/api/api4393dinl1.pdf
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Have Fun
TR
· Thanks for sharing this i did not know that there was such a thing
split the signal and read it
That is something to keep in mind when you need·to do more than one·thing with a input signal
Signals
I do not see any reason·why the chart recorder would work with this·
This a Single 4-20 mA Input & Dual 4-20 mA Outputs unit· Send One Process Signal to Two Locations
S
Single 4-20 mA Input & Dual 4-20 mA Outputs
ingle 4-20 mA Input & Dual 4-20 mA Outputs
S
Single 4-20 mA Input & Dual 4-20 mA Outputs
ingle 4-20 mA Input & Dual 4-20 mA Outputs
DC to DC Signal Splitter, Isolated
DC to DC Signal Splitter, Isolated
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··Thanks for any··that you may have and all of your time finding them
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Sam
Post Edited (sam_sam_sam) : 9/2/2007 10:57:00 PM GMT
Your answer was the closest I wanted. I want to build something to read a 4-20ma signal and interface it to a Basic Stamp (via ADC)
and for a couple of dollars, not $400 like some replies.
I want to use a Basic Stamp to read the output of a chlorine analyzer - Hach CL17. I agree with
FerritMK4 -->
--"you're asking the system to boost its voltage by 5 volts to keep the current up and it's highly unlikely that the system will be able to do that.
I believe the max the chart recorder goes is 10 mg/L but the high alarm is 4.0 mg/L and that is the max I would have to read.
(the chlorine pumps could not dose higher than this)
The low alarm is 1.0 mg/L
and that is more important (this is for drinking water treatment plant- the water has to have some chlorine in it).
So the chart goes from 0-10 but all I should need to read is 0-4 mg/L.
SO lets say I read 0-5 mg/L that should be 4-10ma.
--"Adding a small resistor shouldn't affect the calibration at all.. it's just like adding some lead wire. "
What voltage range for 4-10ma would work for a ..
--"use full differential amps and be careful not to introduce noise."
Do you mean differential op amp ? (I do not have experience with these) and can you recommend a good one?
Would .4 - 1.0 v drop be ok across the series resistor for the differential amp?
Going to stop - getting myself confused.
(FYI - the plant is in the southwest desert and no AC in an uninsulated building - ie very hot environment so I need to use good quality parts)
TIA