Looking for 4-20ma circuits

Fence post error. You wouldn't be a programmer?

You are so full of shit, boy.

I made Infrared thermometers, and many were 4 to 20 mA Linear output. That was nearly 25 years ago. I think the two units pointed at Pad 39A down at Kennedy are of the 4 to 20mA variety. You are a loser.

You're an idiot, still in diapers.

protocol=20

devices)

They ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I will assume that this one was a careless omission on your part.

Cheers, ?-)

Totally agreed. But data link current loops are not the same as industrial automation current loops. Part of the discussion is the differences.

?-)

Most of the ones i have seen are 24 volt based. I have seen as little as

12 V and as much as 48 V required. =20

?-)

bit

been

percentages,

Not at all. It is analog. Then the question is accuracy vs noise.

?-)

24 V is very common in industrial control systems, so it is natural to power the loop from that voltage. With voltage compliance over 20 V and maximum current up to 20 mA, the total loop resistance can be up to 1000 ohms, thus quite long wires (kilometers) can be used between the control room and the sensor in the field, without large conductors. Minimizing the conductor size is important for cost reasons as well as keeping the master cable (control room to factory floor) connecting a large number of sensors at reasonable diameter (below arm diameter) for easier installation.

-48 V to -60 V are typical telecom voltages, so I guess 48 V compliance is available mainly in those systems.

I have seldom seen 4-20 mA loops with only 12 V compliance, but sometimes in 0-20 mA binary Teletype current loop communications.

Just to expand on this a bit- individual devices in the loop typically require a certain maximum voltage drop. If they are externally powered receivers, it might be a pure resistance (eg. 250 ohms), which would drop 5.0V at 20mA. If they are loop-powered receivers, it might be specified as a maximum voltage (eg. 2.5V for an indicator). If they are transmitters, it might be specified as a minimum operating voltage (eg. 8VDC) and a maximum voltage. The compliance is just the loop supply voltage minus the sum of the maximum voltage drops around the loop. You normally want to be able to go a bit beyond the full scale current (eg. to 22mA for a 4~20mA loop) in order to be able to detect an over range or broken sensor situation.

So, for example, with a 24V +/-10% supply, an indicator requiring 3V, a transmitter requiring a minimum of 9V and a receiver with 250R input resistance and 100 ohms of field wiring (total loop resistance), you'd have worst case 1.9 v of compliance @22mA.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

If you did such a thing 25 years ago, I would of thought by now you're language and social skills would have improved?

Your audience much be a bunch of homies learning new ways to not get caught the next time.

Jamie

Seems like I hear some one playing a violin on their fingers? Oops, that may have been me.

Jamie

48 Volt rating devices that I have seen were rated to stand off 48 volts but designed to operate in a 24 Volt world. The idea is to have it survive a phase inversion in a bundle or near by source of 24 volts and end up with 48 volt spur.

Jamie

I remember years ago getting my hands on some original serial equipment that operated a twisted pair at 100 V PP. I think it branched off from the telephone technology back then.

Jamie

"IF"? You are pathetic, boy.

Yeah, we were hoping that you would have though by now as well, but God makes complete and utter retards sometimes, and you just happen to be one.

That would be "your", idiot. Nice job of looking pretty stupid, though.

Well, you can't form a sentence, much less spell it, and the gang boy lingo ("homies") further proves that it is you who has been hanging in the wrong crowd.

Trust me, dumbfuck. You are 100% busted as the total twit you are.

Were you involved in the design of these thermometers?

Absolutely. One of my first engineering positions.

You can FOAD too, little boy. You get nothing further.

Time to make a call to the local sewage removal service, they have a customer waiting in despair. Brown trout everywhere.

Jamie

What precisely did you design?

The "plumber's helper" handle.