Looking for 4-20ma circuits

[Jasen Betts]

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

yeah, I was counting posts instead of rails. and yeah, that's my day
job.

 

[[email protected]]

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.

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.

 

[Spehro Pefhany]

On Sat, 10 Mar 2012 09:41:46 +0200, the renowned

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

 

[Jamie]

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.

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

 

[Jamie]

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

?-)

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


Jamie

 

[Jamie]

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.

?-)

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

 

[Jamie]

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.

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

 

[WoolyBully]

If you did such a thing 25 years ago,

"IF"? You are pathetic, boy.

I would of thought by now

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.

you're
language and social skills would have improved?

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

Your audience much be a bunch of homies

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.

learning new ways to not get
caught the next time.

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

 

[WoolyBully]

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.

 

[Jamie]

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

 

[[email protected]]

What precisely did you design?

The "plumber's helper" handle.