Introduction to Electronics/Lecture Test Equipment

Lecture 1, Basic test equipment

DMM, power supplies, Oscilloscopes, Signal generators

DMM

Digital Multimeters (DMM) are used for measuring voltage, current, or resistance. They often have other features easing lab use, allowing you to measure for capacitance, inductance, and temperature among other things. They have two probes for taking measurements. Care must be taken that they be used properly depending on what is being measured else excessive current may flow through the probes.

When measuring voltage, set the multimeter into a voltage reading mode. In this mode only minuscule amounts of current should be able to flow through the probes. Place the probes across two points in the circuit to measure the voltage across those points. Voltage is always measured between two points. Sometimes its conventional to discuss a voltage at a single point in the circuit, but in this case, the voltage is conventionally relative to the circuit ground.

When measuring current, set the multimeter to measure current. In this mode ideally unlimited current should be able to flow through the probes. Multimeters should have a protective fuse which should blow when measuring current that is too great. Current is always measured through the probes, not across them. Therefore, to measure current through a device, disconnect that device, then touch one probe to the device lead and touch the other probe to the point in the circuit where the device lead was connected. Current should flow through the probes as though the device was connected directly in the circuit.

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  Measurements of voltage by connecting in parallel to the element
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  Measurements of current by connecting in series before the element

Power Supplies

Power supplies provide a stable source of power for circuits. A voltage is specified for the device. Also importantly, current limits are often also specifyable. Mindfully setting maximum current limits can protect circuits when mistakes are made which would cause excessive current to flow.

Oscilloscopes

Oscilloscopes are for measuring time varying voltages, particularly periodic signals. Oscilloscopes have a screen which displays a graph of the voltage over time, called the waveform. Oscilloscope screens are typically divided into squares called divisions. Vertically, the voltage per division can be adjusted to see smaller or larger voltages. Horizontally, the time per division can be adjusted to see faster or slower signals. Digital oscilloscopes often have other features for performing mathematical operations on the input signals.

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