4 - 20 MILLIAMP LOOP

[OLLIE VER]

DOES ANYONE KNOW HOW A 4-20 MILLIAMP LOOP WORKS?
I'D LIKE TO MONITOR GAS PRESSURE, AND AUTOMATICALLY CREATE A 30-DAY CHART [ WITH MAYBE 5 MINUTE READINGS ]
ALSO - AN ALARM FOR LOW OR HIGH PRESSURE
SOMEONE SEZ - USE A TRANSDUCER...
A QUICK CHECK - FOR $20 BUCKS, EBAY SELLS:
.

G1/4 Pressure Transmitter Transducer for Water Gas Oil 4-20mA Output 0-1.6MPA​

.THE GAS LINE IS 80 FT FROM OFFICE / ROUTER / COMPUTER....
I HAVE 9 HARDWIRES BURIED... CAN SUPPLY 110V OR ? TO THE GAUGE / TRANSDUCER.
ALSO, SEND AND RECEIVE THE LOOP SIGNAL....

BUT WHERE TO GO NEXT...? THAT'S THE BIG Q..!
I'M NO TECHIE.... NO GEEK ... IN FACT, TOTALLY LOST...!

NOTE: THIS FORUM GETS CKD IRREGULARLY... EXCUSE ANY GAPS....!

 

[American Locomotive]

Basically, sensors typically come in two varieties:

A) That output a voltage proportional to their reading. So it might be 0v at 0 PSI, and 5v at 100 PSI.
B) Sensors that drive a certain current based on their readings. So it might be 4mA at 0 PSI and 20mA at 100 PSI.

Voltage based sensors are fine for short wiring runs, but in long wiring runs 4-20 mA sensors are better, because voltage drop doesn't matter to the sensor reading. They use 4mA as the baseline for fault detection. They know if the current drops to 0, a wire broke or the sensor failed.

You will need something like this to do what you want: https://www.dataloggerinc.com/product/el-usb-4-usb-current-data-logger/ (although I have no experience with that particular data logger)

You will also need a different sensor. That pressure transducer goes up to 200+ PSI, which wont provide very useful information to you. For the most part, natural gas pressure is going to be 0.25 - 2 PSI. So you will need a sensor with a much lower range.

 

[mcbane]

4-20ma sensors are power guzzlers so you will want to use 2 conductors for power and another 2 for the loop. You need to look at specs on the transmitter you buy and then get a compatible power supply. Typically 24 VDC and you will need 5-10 watts continuous. Dont run AC in the same conduit or you may be dealing with a bit of noise on your signal.

You will also want to get a configurable display that lets you define the range of the sensor so that the digital display shows correct pressures. A common display feature is a separate alarm output and recording of hi and low values since the last reset.

 

[pancho400cid]

Well.....

4 -20 mA is an extremely common analog signal range in industry. The pressure transmitter you describe, when powered by the correct voltage (often 24 VDC but many PT's have different options for supply voltage and some are "loop powered"), and connected correctly puts out an analog signal of 4 mA at a pressure of 0 MPa = 0 PSI. It doesn't say it's an "absolute" pressure transmitter so it is referenced to atmosphere most likely... so it's probably comparing the pressure at the sensing port to the pressure of the atmosphere around it. You need to understand where the reference port is and make sure it's ok for your application... often it's a threaded port, but sometimes it's just a screened hole in the transmitter body, etc.

The full scale pressure of the transmitter is 1.6 MPa = 1.6 megapascals = 232.0604 PSI. I don't know what the pressure range you are trying to monitor is but you need a transmitter that is about 20% higher than the max process pressure or so. In other words if the max pressure is say 10 PSI, the transmitter you describe has way too large of a span.

When the pressure at the sensing port is 1.6 MPa higher than the pressure at the reference/atmospheric port the transmitter puts out a current of 20 mA.

At any pressure between 0 and 1.6 MPa, the current output from the xmitter is exactly proportional to the pressure differential between the sensing port and atmosphere. Basically you "ratio the spans" and add or subtract the zero offset. In your case the scale starts at "0" for pressure and 4 mA for current so there is a zero offset of 4 mA. The "span" is (1.6 - 0) = 1.6 MPa for pressure and (20 - 4) = 16 mA for current.

EXAMPLE: Say the pressure at the sensing port is .95 MPa higher than the ref port.

signal current I = [(.95/1.6) x (20-4)] + 4 = 13.5 mA

You need a chart recorder or analog data recorder or any of literally thousands of devices that "understand" a 4-20 mA signal and will collect the data and let you scale it, display it, or even write it on an old school strip chart that literally records the input with a pen and charts the scaled data.

Also - The description you posted says "G1/4". "G" is a "gas" connection common in Europe... it is one form of BSPP threads. It would be easier to plumb up if you find an transmitter that has NPT threads.


...

 

[OLLIE VER]

WOW !!! V V V HELPFUL - THX EVERYONE - THAT SHOULD GET ME WELL ON THE WAY...!

PRESSURE RELIEF IS SET AT 60# [ NOT absolute pressure - GRACIAS PANCHO..!]....

WORKIN RANGE IS 0 - 40#
SO... 0.5 MPa transmitter = perfecto....

All right - now.....
Gonna ck out the datalogger link ...THX, Amer. Locomotive..!

NPT would be Much better... THX again Pancho.!

Typically 24 VDC and you will need 5-10 watts continuous. - GREAT..! THX SO MUCH, MCBANE..!


Hope I can return the favors to you'all sometime....!

It'll probably be a few days before I get back to this project.... but I'll try to update when it's all workin.....!

THX
THX
THX
T
H
X

 

[engineer2]

You can buy an indicating pressure transmitter with alarms and 4-20 mA output. Google F16DAR.
For a reasonable data logger look at Adam or Hobo.
Remember with a 4-20 mA loop one, and only one, device must power the loop.
If this is natural or a flammable gas, you may need an intrinsically safe 4-20 mA transmitter or barrier with your display and alarms outside of the hazardous area.

Glad to see we have a few analog process signal guys here!

 

[mike93lx]

Interesting thread.

But why are you yelling?

 

[DevinJ]

When you say "gas pressure" do you mean like natural gas at your house? If you're monitoring natural gas pressure it's only like .3 psi after the regulator. You'll only need like a 0-1 psi sensor.

If you're measuring it before the regulator that is usually the gas companies line. I don't know if I'd be messing with that.

 

[wyliesdiesels]

youre getting 40-60Lbs pf pressure? what kind of gas is this?

 

[DevinJ]

youre getting 40-60Lbs pf pressure? what kind of gas is this?

That's what I'm thinking. He wasn't very specific in his post. Not to question his project but what it the point of monitoring the nat gas pressure?

 

[engineer2]

30 psi is typical incoming pressure for an industrial user of natural gas (i.e. industrial furnaces and large facilities). Not uncommon for a company to monitor the incoming pressure. Some industrial users even contract for an uninterruptable supply.

However, for a residential user, messing with the gas company's equipment is ill-advised.

 

[OLLIE VER]

YES - IT'S NATURAL GAS... WELLHEAD GAS DIRECTLY TO IRRIGATION ENGINE..

OOPS! YELLING AGAIN - IT'S JUST A HABIT..!!!

Amer. Locomotie's link above leades to:

Lascar EL-USB-4​

• 4-20mA current loop measurement range
• Logging rates between 1s and 12hr
• Store 32,510 readings
• Connection via two screw terminals
• USB interface for set-up and data download via PC (not Mac compatible)
• User-programmable alarm thresholds
• Status indication via red and green LEDs
• Supplied with replaceable internal lithium battery and Windows control software

• Download Specification Sheet

$90.00

 

[engineer2]

That should work. According to their wiring diagram, it looks like it provides power to the current loop, which is unusual for a USB powered device.

Is your wellhead gas clean or acidic? Not uncommon to find a bit of sulfuric acid in raw gas. Stainless should be OK with low concentrations of acid, but check online to be sure.

Make sure you have no leaks when you wire it up or we'll be reading about you in the news!

 

[OLLIE VER]

Gas is metered at wellhead - with an old Old OLD Barton meter. [Paper wheel chart...!]
AMAZING ACCURACY +/- 1.5%......!

Then metered again at individual irr. engines - with Roots meters....which count 3 X faster at 15# than at 35# - so it's NOT accurate to just average that to 25# ...
IT TAKES A WEIGHTED AVG - ADJUSTED BY THE AMOUNT OF TIME AT EACH PRESSURE.

A big spreadsheet does that calculation, but it's only as good as input - and an automated continuous pressure reading is the CAT'S MEOW...

Without that, I'm out readin gauges several X / day....

Of course, I'll still be manually transferrin from data logger to spreadsheet, but that can be done occasionally / end of month when reports are made....

Of course, one of them tech-savvy Remote Support Gurus could probably link data logger to spreadsheet....!
______________

ANOTHER OPTION WOULD BE TO INSTALL GAS PRESSURE REGULATORS DIRECTLY UPSTREAM OF EACH ROOTS METER, AND SUPPLY A STEADY 10#...

Roots Meters are super accurate at constant pressure...
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THE HI-LOW PRESSURE ALARMS ARE ANOTHER HUGE REASON TO MONITOR PRESSURE....
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THX AGAIN, EVERYONE...!