How to monitor AC voltage and current with your RMS unit.
Our remote voltage monitoring boards have built-in DC voltmeters that can measure +/- 100
volts. If all you need to do is sense the presence of AC power, then this is easily done by
using a common AC to DC wall transformer as shown below. Plug the transformer into a wall
outlet or generator outlet, then attach the wires to any of the RMS voltmeters to monitor
if AC power is available. NOTE: Make sure the transformer outputs DC voltage not
exceeding 100 volts.
But what if you need to monitor the actual AC voltage or current?
The aim of this project is to show you how to monitor AC voltage and current using the RMS
remote monitoring system. Please read the disclaimer at the
bottom of this web page before proceeding.
Measuring AC voltage
Two major problems to overcome are:
- The voltmeters on the RMS board can only measure DC voltage.
- The voltmeters on the RMS board have a limit of +/- 100 volts.
What is needed in this case is a way to convert the AC voltage to a DC voltage that
can be measured by the RMS board. To do this we need to use a transducer. A transducer is a
device that converts one type of energy to another. The transducer we tested with is the
model number AVT-300c from Ohio Semitronics shown
The AVT-300c can take 0 - 300 volts AC input and will output a relational 0 - 10 volts DC.
This makes measuring AC voltage by the RMS board easy. Hook up the AC wires to terminals 3
and 4 on the transducer. Hook up the output voltage wires from the transducer terminals 1
and 2 to any of the RMS DC voltmeters. To figure out the AC voltage, simply take the
measured voltage from the RMS voltmeter and multiply the reading by 30. The RMS board makes
this easy by providing an adjustment multiplier for each voltmeter.
Several transducers are available from Ohio Semitronics that have different AC input voltage ranges. AC voltage ranges include 90, 150, 300, and 600 volts.
Measuring AC current
Measuring AC current is also easy using a current transformer.
A current transformer is used for measurement of alternating electric currents.
The current transformer shown below is a non-invasive split core current sensing device. Several models
are available that measure up to 200 amps AC and output 0 to 10 volts DC. 4 to 20 ma output
versions are also available. Clamp the current transformer around one power wire of the current source you
want to measure. Hook up the output wires from the current transformer to any of the RMS DC voltmeters. To
figure out the AC current in the case of a 100 amp current transformer, simply take the measured voltage
from the RMS voltmeter and multiply the reading by 10. These current transformers can be
Automation Direct. Be sure to purchase models that output DC voltage. For models that
output 4 to 20 ma, an adapter can be found here.
WARNING: Electrical projects are inherently dangerous, and even the most benign task can
cause serious injury or death if not done properly.
ALWAYS READ AND FOLLOW INSTRUCTION MANUALS AND SAFETY WARNINGS OF TOOLS OR EQUIPMENT.
You must be particularly careful when dealing with electricity - always use common sense. Any advice, guidance or other information provided on this website or within any of our publications cannot completely anticipate your situation. If you are at all unsure about completing any aspect of this or other project, consult a qualified electrical contractor to perform the service(s) for you.
ALWAYS follow electrical code requirements specific to your area, and before undertaking any electrical project, contact your local electrical authority and your insurance company to ensure that you comply with all policies, warranties, regulations and authorities concerning this work.
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EtherTek Circuits started its business in 2001. Ever since we have provided remote monitoring and control solutions for Remote Tower Sites, the Oil & Gas industry, Telemetry systems for Agriculture, Municipalities, Mines, Solar Farms, Hydro Plants, and the Military.
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