I’m going to show you an easy to follow 5 step guide
to using a fluke 789 process meter - for sourcing or simulating 4-20mA loops,
perfect for a whole host of instrumentation, calibration and fault finding needs.
Quickly, before we move onto to the steps on how to use the fluke 789.
We should discuss the difference between sourcing and simulate modes.
Transmitters and other sensors that give 4-20mA signals are connected to a plc or other input
device that reads the current within the loop. These current loops are usually 24v DC powered.
These Instrumentation loops can be either have the 24Vs powered from the input card or
the transmitter is externally powered and it provides the 24Vs for the loop power.
When using a process meter in place of a transmitter to test a loop you
will need to use it in a different mode depending on what is powering the loop.
If the transmitter was supplying the loop power, you’ll need to source the loop.
If the input card or isolator is powering the loop, you’ll need to simulate the loop.
Lets now lets look at the steps you’ll need to source or simulate,
afterwards I’ll go through a few tips how to identify how a 4-20mA loop is
setup so you will know what mode to use. Remember electricity is dangerous, so only
work on equipment you are competent to do so! And always check the voltages you are working with.
For sourcing 4-20mA on a loop that is powered from the transmitter follow these steps
Step 1 – Isolate your transmitter loop and disconnect your transmitter at the head.
Step 2 – Put the meter into mA loop power mode. Step 3 – Connect the red probe to the left loop
power port on the meter and connect to the positive wire going back to your input card.
Step 4 – Connect the black probe to the mA output port
and the negative wire going back to your input card.
Step 5- Deisolate the loop, congratulations you are now sourcing the loop and can change
the current setting with the COARSE and fine, up and down arrows to step through different current
values between 0- 20mA Simulate 4-20mA
For simulating a loop that is powered from the input card or barrier follow these steps:
Step 1 – Isolate your transmitter loop and disconnect your transmitter at the head.
Step 2 – Put the Meter into mA manual mode. Step 3 – Connect the red probe to the mA port
on the meter and connect to the positive wire going back to your input card.
Step 4 – Connect the black probe to the Common port on the meter and connect to the
negative wire going back to your input card. Step 5- Deisolate the loop and you are now
simulating current in the loop. Just like when sourcing you can change the current
setting with the COARSE and fine buttons. Auto Sinking – Its worth knowing that the
Fluke 789 has an auto step functionality that is really useful when loan working on 0-20mA or
4-20mA loops. This mode will run the meter through the full current range, either in a nice smooth
sweep, or predetermined steps. Simply connect to your input card the same way as source or sink
but put the meter into the mA step mode. Use the blue button to change through the different modes.
If you are unsure if the loop you are working on is source or simulate, isolate the equipment
at the head and test for voltage first on the head and then on the loop. If the voltage is
on the transmitter head then you know you need to source. If the voltage is on the input card
then you need to simulate. For the other modes of the meter
such as continuity and voltage, check out my other video guide on a fluke 117
that contains all these same modes. Check out the link in the description
for the latest price of the fluke 789 on Amazon. If you do want to purchase the
fluke 789 or anything else on amazon for that matter then using this link will help support
the channel at no extra cost to yourself. I hope you have enjoyed the video and
remember to like and subscribe for more great content in the future.