Application Note

Troubleshooting 4 to 20 mA
process control systems
without breaking the loop
Where pH is important
Anyone who works in any kind
of manufacturing plant knows
that nothing can ruin a day faster
than unscheduled downtime.
The lost production time means
lower output, which can have
a sizable price tag. In a process
plant that lost productivity can
be magnified because an entire
batch of a product could be
ruined if the outage occurs at a
critical point in the process.
Keeping processes up and
running properly requires
efficient and accurate trouble-
shooting tools. An instrument
technician in the oil, gas, and
chemical industry for the last 15
years knows that only too well.
He’s responsible for maintaining
and troubleshooting pressure,
flow, temperature, and pH trans-
mitters in a chemical processing
plant. As you might expect, pow-
ering down the equipment is the
option of last resort.
He has been using Fluke tools
since he first started in the field.
“When you’re working in process
control, you need to have equip-
ment that you trust; I don’t know
an instrument tech who doesn’t
almost exclusively use Fluke for
all of their test equipment.”
When he saw the Fluke 773
Milliamp Process Clamp Meter at
a trade show in early 2011, he
saw huge possibilities for using
it in the plant where he works.
The 773 measures milliamp (mA)
signals without breaking the
loop, which makes it ideal for
troubleshooting the transmitters,
valves, and programmable logic
controllers (PLCs) found in pro-
cess plants. It also sources and
measures dc voltage, so it can be
used to troubleshoot voltage input
and output devices. The clamp
section of the meter is detach-
able and can be used as a remote
jaw, connected to the main body
by an extension cable to make it
easier to take measurements in
tight spaces.
Finding intermittent
problems without break-
ing the loop
“The biggest thing I’ve found
with the 773 is that I can
troubleshoot a live device without
having to power down, and pos-
sibly miss something going on in
the process. When you’re dealing
with chemicals you can have an
ongoing problem that’s very quick
and intermittent and eventually
leads to a single major break-
down. I can take the 773 to the
process instrument, hook it up,
observe the output, and compare
it to an indicator. It can eliminate
the transmitter as a point of error
The clamp section of the Fluke 773 clamp meter is detachable, connected to the main body of
the test tool by an extension cable.
in the loop using mA simulate,
and the clamp meter provides
its own 24-volt loop power for
performing substitution and isola-
tion tests.”
Before using the 773, he had
to go to the power supply, de-
energize the circuit, go back to
the instrument, hook the meter
up in series, and then go back
and re-energize the circuit and
do the calibration check. “Every
time I don’t have to power down
an instrument, it probably saves
me three to four minutes per
instrument, and that adds up
because every hour that one of
our processes is down runs sev-
eral thousand dollars.”
Application Note
From the Fluke Digital Library @ www.fluke.com/library