As a technician you'll be frequently working on electronic equipment, you'll likely be performing
calibration testing and fault finding on these electronic loops and circuits.
In order to understand exactly what is happening within these loops and perform your role as a
technician, it's vital you understand how to use a digital process or multimeter in order to measure
and simulate loop characteristics such as voltage, current and resistance within these circuits.
In this video I'm going to teach you exactly how to do that using a fluke 117 multimeter, which is
an extremely common multimeter used within industry, although other meter manufacturers
use similar symbols and functions so this guide should assist you with most meter types.
It is important to remember that electricity can be extremely dangerous and in the worst cases
cause death for that reason only work on systems that you have the competency to do so and ensure
to follow local legislation and guidance and always isolate loops electrically where applicable.
This is a fluke 117 multimeter it is a quality multimeter that has all the basic functionality
for taking measurements from an electronic loop. It does not have the functionality to simulate
currents that you will need for calibration of input devices and some fault finding,
for that type of work you'll need a process meter like the fluke 789. I'll go over its functionality
in the next video. Let's go over the components of the meter. Here is the screen or readout, it shows
you the value of what you are measuring. This could be voltage, current, resistance, frequency
or capacitance. The readout will give you units, the scale and other visual information
about your measurements. Below the readout we have several buttons that give different functionality.
Some buttons have varying functionality dependent on your mode selection but we will go over the
main functions here. The hold button can be used during measurement readings to freeze the display,
this is useful if you have a varying reading that you need to record at a certain time
or if loan working, will allow you to free both hands and record the reading on paperwork such
as calibration documentation. The min max button allows you to enter a mode that
will record the highest lowest and average reading recorded since entering the mode.
The range button will allow you to enter either an auto ranging or manual ranging mode, for most
applications auto ranging will be best and will select the unit value most appropriate. It is most
notable during resistance readings, where you could be reading anything from ohms, kiloohms or megaohms.
The yellow button is used to give alternative function, if you look at the selector dial you'll
notice certain symbols are in yellow. The yellow button allows you to utilize these functions.
The lamp button will give you a backlight to the display, perfect for working in cabinets that may
not have decent lighting. The selector dial allows you to change between the different operating
modes of the meter, depending on the specific task that you are carrying out. Look at the
different symbols around the outside of the dial, these indicate the function of the meter. We will
go through all of these symbols in detail later in the video. At the bottom we have the ports where we
connect our test leads, depending on the mode, we will be connecting our leads in different ports.
Don't worry though, I'll show you exactly where to connect the probes for each mode when carrying out
tests. Here is an example of a set of probes or test leads you will use with a multimeter.
These allow you to connect the meter to a circuit electrically
at different points to take the readings you need. Probes usually come in two specific types,
probes that allow us to hold the probes on terminals or other electrical conductors
or clips that are used to connect to disconnected wires or earth points.
Before using your meter you should give it a once-over and ensure it's in good working order.
Check to see if the equipment is within calibration, you will often find a calibration
sticker or label on the equipment this is often under the protective casing.
Check the leads for any damage to the insulation. It's important to check the type of leads that you
are using, depending on the country you are working in there could be guidance or legislation that
states your test leads have to be fused and meet certain quality standards. Here in the UK we have
the GS38 guidance notes that lay out what British standards test probes should be manufactured to.
Always check your local guidance. Next, let's go through each mode on the rotary selector
and talk about what that mode is and what you might be testing with it as a technician. Let's
look at this symbol on the mode selector. The "V" stands for voltage, more specifically this mode is
AC or alternating current voltage, you can tell by looking at the wavy line above the "V" this is how
the sine wave of AC current would look on a scope or if voltage were graphed against time. Voltage is
the potential difference of energy between two conductors. If these conductors are connected we
will form a circuit and current flows. AC voltages you would be typically measuring in industry,
depending on your region are: Single phase at 110 to 120 or 230 to 240 and three phase 380 to 415 volts.
These voltages are typically found in supply type applications such as equipment power
supplies, contactors, cabinet lighting and heaters. They are rarely used in signal applications.
For our probe configuration, our black probe would be connected to common and our red probe connected
to the "V" port. Our probes connect between whatever two conductors we are checking voltage between.
In single phase applications this is usually between live and neutral
and three-phase applications we will be measuring between the phases or phase to neutral or earth.
Looking at the Hertz symbol in yellow on this mode, if we press the yellow function button
while measuring an AC voltage, we will be able to determine its frequency measured in Hertz.
A "hertz" is how many times a second the alternating current voltages cycles, think back to the wave
symbol. Typical power supplies in the UK and Europe and most of Asia are 50 hertz. Whereas
voltages in the US are usually 60 hertz. This mode is for measuring DC or direct current voltage.
Notice there is no hertz function available in this mode this is because this mode is for
measuring DC and there is no frequency as the current continually flows in a single direction.
Some equipment may be powered by dc voltages such as PLC equipment or solenoid supplies, especially
if these are battery powered or battery backed, but they are also found in the signal applications
such as the voltage in a 4 to 20 milliamp transmitter loop for analogue signals, and
also in digital signals where equipment is looking for voltage to be present or not
to determine an input state. Common DC voltages we may be testing for are 5, 12, 24 and 110 volts DC.
Our probes are connected to common and the "V" ports just as with the AC voltage and again our probes
are to go between the positive conductor and zero volts or negative conductor. Millivolts are almost
exclusively used for signal measurements, a prime example is a thermocouple that will give
us a milli or micro volt reading depending on the temperature of the probe. Using the shift button will
give you the function to measure DC millivolts. As in other voltage measuring modes our probes
are connected to common and volts. In the auto volts selection mode, the meter will automatically
detect the voltage type and change the units accordingly, again probes are in common and voltage.
Our last voltage measurement mode is the volt alert mode. In this mode the meter can detect
AC voltage without the use of test leads. Simply place the top of the meter near a live conductor,
if a voltage is detected the meter will illuminate and a beeping sound will be present.
Don't use this mode as proof there is no voltage and always carry out full test for dead with a
proving unit before touching any conductor. We can use the meter to measure resistance, resistance is
measured in ohms and as its name suggests it is the measurement of the restriction to the
flow of electricity. The easier the current flows through a conductor, then the lower the resistance.
Long low diameter cable will have a high resistance whereas a short high diameter cable
will have a low resistance. In instrumentation the types of things we would be measuring the
resistance of are point-to-point signal and power cables, relay and solenoid coil resistances,
resistance between earth or bonding straps, testing of fuses. To test for resistance we need
to have our probes connected to the common and ohm symbol. Our probes are red and black. For resistant
measurements it does not matter what color probes we connect to the earth port on the meter.
However it is good practice to connect the black probe to the common and red probe to
the ohms connection. This is because when measuring voltage, the polarity is important.
If you were to look at the readout you will see the resistance reading is showing open circuit. To test the meter
is functioning correctly and our leads fuses have not blown a quick continuity test is useful.
Connect the probe ends together, the meter display should read a small ohms value of around two or three ohms.
This is the resistance of the test leads, it is useful to take this reading as
a reference as the resistance will need to be subtracted from any part of a circuit you test.
Now you can repeat the test with any part of the circuit you wish to measure.
The continuity mode will beep whenever there is electrical continuity between the probes this function is
useful for fault finding or checking fuses. Probes are in the common and continuity ports, as shown.
In this mode the meter can be used to detect if a diode is functioning correctly. A diode is a device
that allows current to flow in a single direction and can be either forward or reverse biased.
If connected to a diode in this mode, the meter will read a small voltage if the diode is allowing
flow from the red probe to the black. It will show open circuit if the diode is not allowing current
to flow. Diodes can be found in dual power supply setups and for some hardwired logic applications.
If we press the function button while in this mode, it will allow us to test for capacitance
of a capacitor, from nano to micro Farads, which is the unit of capacitance.
To test the capacitance simply measure across each leg of the capacitor. You won't frequently be
taking capacitance readings as a technician as this is normally reserved for old electronic
board repair type applications, where you may be looking to measure specific capacitor readings.
The fluke 117 can be used to measure currents of up to 10 amps AC. Currents are normally measured to
check the load of supply circuits. In order to do this you would have to isolate the circuit, pick a
point to break the circuit and insert the meter in series with one of the legs. Notice the port
used for current measurements are different from voltage measurements. The polarity doesn't matter
in AC current applications. Be careful not to leave exposed conductors while the meter is in series,
use connector block wherever applicable to help avoid shock. Reconnect the circuit and take your
current reading, if the current is above 10 amps the internal fuse will likely blow to
protect the device. As with the AC measurements, the frequency of the voltage can be checked
in this mode via the use of the yellow button. You can also measure DC voltage as with AC, you
might need to test power draw of supply voltage. Dc currents are often used as signals too, such as
4 to 20 milliamps for a pressure or temperature transmitter. You would measure the current exactly
the same as the AC voltage by isolating the loop and going in series with the circuit.
I want to finish up with a simple pressure transmitter loop we used in a previous video
and then show how we would test for voltage and current with the multimeter. Here is our circuit,
this is a 4 to 20 milliamp transmitter powered by 24 volts dc from a barrier, that then passes
the signal back to the PLC. If we were to measure voltage at the transmitter head we would put our
meter into volts dc mode and connect our red probe to the positive terminal and our black probe to
the negative terminal. We would then be reading the potential difference across the transmitter.
If we wanted to measure the milliamp current within the circuit we would first put our meter
into current dc mode, we would then isolate the circuit by powering down the barrier,
then break into the loop. Because we are measuring current it doesn't matter where in the circuit we
take our measurement from as current is always equal in a two-wire loop. It's normally easiest
to do this at the transmitter or head. Disconnect the positive terminal, connect the positive probe
to the supply coming from the barrier that we have just disconnected, connect the common
lead to the positive terminal of the transmitter. The meter now forms part of the circuit when we
re-power the loop and we will get the current readout of the loop. If you are interested in
prices of the fluke 117, check a link in the description to Amazon for this meter. If you do
decide to make a purchase please do so and go through the link as i'll get a small commission
for pointing you over and it won't cost you any more than if you are navigated there yourself.
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