Intro Digital multimeter

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Intro Digital multimeter#

This intro supports labmanual 1A

There are two digital multimeters: a handheld one, and one in the caddie.

  • Leave the big Siglent multimeter (not carryable) in the caddy, there are cables at the back which should not be taken out.

  • The handheld (red) multimeter can be taken out of the caddy.

Spend some time getting familiar with these devices. Ask the TAs if you have doubts.

Watch the following movie clip to get introduced to the multimeter

## SCR-DMM

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Siglent multimeter:#

Also have a look at the quick start manual: https://int.siglent.com/u_file/download/24_12_25/SDM_Series_QuickStart_EN04B.pdf

or the full manual: https://telonic.co.uk/jg/wp-content/uploads/2021/08/Siglent-SDM3055-Multimeter-Manual.pdf

Voltage measurement#

  • First connect all wires before switching on the output of the supply in the to-be-measured circuit

  • Use the red voltage connector (top right), and the black COM connector.

  • Select either AC voltage, or DC voltage (white buttons).

  • when set correctly: switch on the output

  • when switching from voltage to current measurement: remove the wires, as you’ll use another input pin

AC=alternating current, DC= direct current constant value

Note: the voltage is measured in parallel with a circuit!!

Current measurement#

  • First connect all wires before switching on the output of the supply in the to-be-measured circuit

  • Use the red current connector (bottom option!), and the black COM connector.

  • Select either AC current, or DC current:

    • use the blue Shift/Local button, and then find in blue letters DCI (just above the white DCV button)

    • with Shift, you the blue description above each white button becomes active

  • when set correctly: switch on the output

  • when switching from current to voltage measurement: remove the wires, as you’ll use another input pin

Note: the current is measured in series with a circuit, never in parallel!!

WARNING!!

  • Measuring current should be done carefully since the DMM is part of the circuit.

  • A common mistake is to leave the cables or test leads in the current input terminals and measure voltage.

  • Remember that the current terminals are connected to a very low resistance (Shunt resistance).

  • When connected in parallel to your circuit, high current will flow through the DMM.

  • This can damage both the multimeter and the circuit.

  • If you are not sure about how to connect your multimeter, please ask one of the TAs.

Resistance measurement#

  • Switch all sources in the to-be-measured circuit off

  • Use the red voltage & resistance connector, and the black COM connector.

  • Measure the resistance (press the \(\Omega\) 2W)

Other measurements#

Check out the manuals to find out on additional options such as:

  • measure capacitance (white button with capacitor sign)

  • measure frequency (shift + Freq)

  • test a diode (shift + blue diode above Cont)

  • Use dual display, by:

    • select your main display, for example frequency

    • press Dual

    • select a second display, for example AC voltage

    • possible selections:

      • all combinations with AC/DC V&I

      • main: FREQ/PERIOD, vice: ACV

      • main: AC V&I, vice: FREQ/PERIOD

Digits& Accuracy#

The formula for the accuracy of the 5½ digit DMM is specified as ±(0.025% + 0.005%) = ±(reading%+ range%) by the manufacturer.

What do 5½ digit mean:#

Note: the 1.2V is the reading, which is smaller than the 2 or 20 V range.
For a 2V range measured with a 3½ digit DMM, the maximum is 1.999 V, the minimum is 0.001 V.
For a 20 V range measured with a 3½ digit DMM, the maximum is 19.99 V, the minimum is 0.01 V.
For each range with the same number of digits, you have a different number of digits behind the decimal point.

The number before the decimal point can be either 0 or 1 (hence ½ digit).

Accuracy#

For 1.2V, the accuracy is 0.4 mV. (± 0.025% * 1.2V + 0.005% * 2V).

What would be the accuracy of a 1.2 V reading with a 20 V range? Is that better or worse than reading it on a 2 V range?

Automatic versus manual range#

In the bottom middle you find a Range button, which lets you toggle between automatic or manual range.

Once set to manual range, you can adjust the range with the + and - button.

Handheld DMM#

  • Use similar connectors as for the bigger DMM:

    • you can also measure AC/DC current and resistance.

    • take the same care of selecting the correct input pin as for the Siglent multimeter

    • Connect the black wire to the COM pin of the handheld DMM

    • Connect the red wire to either the right red Voltage/Resistor input pin, or the left yellow current pins (two options: mA/\(\mu\)A or 10 A) of the handheld DMM

  • Turn the knob of the handheld to whatever you want to measure

    • V= is DC voltage, and V~ is AC voltage.

Measure current and voltage at the same time#

There are multiple solutions measuring current and voltage at the same time:

  • Use handheld and regular DMM

    • When choosing which meter to use for current or voltage, note: The large DMM has more digits, and therefore better accuracy than the handheld one. This might be of influence when choosing which meter to use for the current (or voltage).

  • both on the siglent multimeter in Dual mode

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