Digital multimeters (DMMs) are multipurpose devices used to measure several different circuit parameters. Commonly available DMMs measure the following quantities:
Many DMMs are capable of measuring additional quantities, such as frequency, conductance, and inductance. In this exercise, we will only concern ourselves with the measurement of constant voltages, constant currents, and resistance. Some brief definitions relative to these parameters are provided below; somewhat more in-depth background information is provided in the links to the right.
DMMs are extremely common devices, and a variety of them are readily available. They can be broadly categorized as either laboratory/bench systems or hand-held devices. Bench systems will generally have greater capabilities than hand-held DMMs and typically better accuracy, but are not easily portable. Hand-held DMMs are battery operated, making them readily portable and correspondingly popular. The basic operation of the bench and hand-held DMM models are similar.
The operation descriptions provided in this project are for the hand-held DMM, which is available for purchase on Digilent's website. This is a relatively inexpensive DMM, and has all the capabilities necessary for the labs (which are also available on Digilent's website). The instructions provided here should be helpful regardless of the DMM model you have.
All DMMs provide the same basic components:
These components are indicated on Fig. 1. Since DMMs are intended to perform a number of functions, there are a variety of combinations of configurations for both the dial, which selects the function; and the ports, which are used to connect the DMM to the circuit. The dial position must be consistent with the ports being used.