4 to 20 What!?!
4 to 20 What!?!
(OP)
We have this English Oxygen sensor that puts out 4-20mA.
(see link below)
-BUT!-
It only puts it out into absurdly low impedance, like a DMM.
If you put it into 10ohms the 20mA sags to perhaps 7mA.
Put it into 500ohms and you get maybe 0.1mA.
It states 10 - 35VDC this is at 12VDC. If you crank up the supply to 30V it makes about a 10% improvement.
Is this thing goofed up or is this a type of 4-20 device I've not heard about?
And what's with that crazy output impedance?
(see link below)
-BUT!-
It only puts it out into absurdly low impedance, like a DMM.
If you put it into 10ohms the 20mA sags to perhaps 7mA.
Put it into 500ohms and you get maybe 0.1mA.
It states 10 - 35VDC this is at 12VDC. If you crank up the supply to 30V it makes about a 10% improvement.
Is this thing goofed up or is this a type of 4-20 device I've not heard about?
And what's with that crazy output impedance?
Keith Cress
kcress - http://www.flaminsystems.com





RE: 4 to 20 What!?!
Cheers
Harry
www.tynevalleyplastics.co.uk
RE: 4 to 20 What!?!
Since when do current outputs have 15 Meg ohm output impedances?
How much current does it really supply into a DMM? a full 20 mils?
Maybe it's really a voltage output, and 'mis-spec'd'? or the voltage output model mislabeled?
RE: 4 to 20 What!?!
12V at 4 ma should allow a maximum loop resistance of 600 Ohms minus the resistance of the transmitter.
I wonder if the 15 M Ohm is milli Ohms instead of 15 Meg-Ohms.
That would give a voltage drop across the transmitter of 0.06 millivolts at 4 ma. That seems low.
After a short break to check Omega.com, I wonder if you have just the sensor, and not the complete sensor-transmitter package.
Some of the Omega packages have a conventional 4-20 transmitter which is connected to a sensor, but the voltages/currents in the connection between the transmitter and sensor aren't specified.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 4 to 20 What!?!
RE: 4 to 20 What!?!
TTFN
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RE: 4 to 20 What!?!
RE: 4 to 20 What!?!
TTFN
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RE: 4 to 20 What!?!
Thanks for the communication offer Pud! Lets see what transpires tomorrow.
danw2; It really supplies the full 20mA to the DMM.
Bill, You have several good points. (as usual) Might be 15mOhms not Mohms. That would make much more sense.
Otherwise I agree the thing is messed up or needs an interface board. That is entirely it for the companies (*&^%}*^%( POS data sheet. Really really bad. Personally I would not even use a product that had so little useful info avaiable but what's a body to do.
dpc; IR is correct I O U volts.
ilj; interesting point, but...
Keith Cress
kcress - http://www.flaminsystems.com
RE: 4 to 20 What!?!
Think back to your school days: an ideal current source has infinite impedance.
To me the spec makes perfect sense and is an indication of how good the current source is.
That being said, I'd say your device is kaputt.
Benta.
RE: 4 to 20 What!?!
The unit was believed to be a 4 wire unit. The leads brought out to us were from the factory test pins and have been used this way for over 10 years.!!!
In fact, the device is really a 2 wire unit and you put the sense resistor in series with the power leads as you would expect.
Cheers.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 4 to 20 What!?!
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 4 to 20 What!?!
www.MaguffinMicrowave.com
Microwave and wireless design consulting
RE: 4 to 20 What!?!
Why did you reach this conclusion? HART just superimposes data onto a standard 2-wire 4-20mA loop.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: 4 to 20 What!?!
RE: 4 to 20 What!?!
I would use an indicator with an internal loop power supply.
RE: 4 to 20 What!?!
Roy
RE: 4 to 20 What!?!
To reiterate. It was two miswirings strung up against years of using it the wrong way in a system that didn't care. Now as we were handed the device, (all nicely miswired), and added it to a "normal situation" the results were very confusing.
The system is working fine now.
roydm; I saw that as a jury rig hung in the chain for testing years ago but never thought to add it to a design! I like it a lot as it works well.
Keith Cress
kcress - http://www.flaminsystems.com