Model 98025 is a popular seven-function Cen-Tech digital multimeter, and if you know how to use it, you'll know how to use any seven-function digital multimeter with perhaps one exception. The Cen-Tech 95683 is a special case. It comes equipped with a clamping jaw that allows the device to measure current flow up to 1,000 amps in a live conductor.
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It's always a good idea to consult your Cen-Tech digital multimeter manual. It contains detailed instructions that can't be covered in a short expository.
The Seven Functions Most Digital Multimeters Perform
A seven-function digital multimeter can measure the following:
- Current up to 200 mA
- Current higher than 200 mA
- Diode condition
- Transistor condition
- Battery charge
Each function has a particular setting on the dial, and within each function are a number of sensitivity settings. When choosing a function, it's important to select a sensitivity just above the expected magnitude of the measurement. If you choose a sensitivity that's too high, you won't get an accurate reading, and if you choose one that's too low, you won't get a reading at all.
When using the transformer jaws on model 95683 to measure very high current, you need to select a very low sensitivity because you're measuring large current.
Ports and Leads
Every multimeter has two leads. One is black, and one is red, and they may have alligator clips that clamp onto the wires you're measuring or straight tips that require you to hold the leads when making measurements.
The leads are equivalent, but by convention, the black one goes into the COM port. That leaves two other ports for the red one, and for most measurements, you use the VΩnA port. Use the 10A port only when measuring current larger than 200 milliamps.
Seven-Function Digital Multimeter Dial Settings
The dial settings are mostly self-explanatory as long as you understand the meanings of the symbols.
- Ω means ohms, which is a measure of resistance. Set the dial here when you want to measure resistance or circuit continuity.
- DCV means DC voltage.
- ACV means AC voltage, which may be denoted as V with a wavy line over it.
- DCA means DC current.
- ACA means AC current, and this may also be denoted with a wavy line.
- A cross with a horizontal arrow on the left axis of the symbol for a diode. Use this when testing a diode.
- hFE is the transistor setting. Select this when testing a transistor. The transistor plugs into a special seven-pin port on the front of the meter.
- A horizontal line with two vertical lines through it signifies the battery test area. Select it when testing batteries.
Making a Measurement
You make a measurement by choosing the appropriate dial setting, plugging the leads into the appropriate ports, holding them in contact with the wire and noting the numbers on the LED screen. The exceptions are when you plug a transistor into the hFE port or you use the clamping jaws on the 95683. In both exceptions, you should remove the leads from the ports to avoid a faulty reading.
When measuring current and voltage, the circuit should be connected to power with the power on, but when measuring resistance or continuity, the circuit should be disconnected from power. The meter has its own power source, and it sends a small current through the circuit. If the circuit already has power, the resistance reading won't be accurate, and the extra current could damage the meter.