A capacitance meter is a specialized piece of testing equipment. It is used to determine the potential capacitance of a given capacitor. These meters come in many varieties and sizes in order to measure capacitance in many different contexts. The ability to measure capacitance is included in some but not all multimeters.
Physically, most of these devices are simple handheld units with two leads that can be connected to a capacitor for testing. Older models used an analog display, but these are now quite uncommon. Specialized types of capacitance meter, especially those for testing very large or very small capacitors, are likely to be larger units with different types of specialized probes appropriate for the type of measurement that a particular capacitance meter is designed to take.
Electrical charge can be accumulated and stored temporarily in a capacitor. Capacitors hold energy in the form of positive and negative charges on two conductor plates that are separated by a resistor. A field forms between these elements, and can hold a charge. This charge can then later be released. Capacitors are not as useful for long-term energy storage as are batteries but are able to discharge stored energy much more rapidly, making them useful for certain applications that demand such rapid discharge but also potentially dangerous.
The ability of a capacitor to accumulate an electrical charge is termed its capacitance, and it is this value that is measured by a capacitance meter. The simplest method of measurement is to apply an electrical current to a discharged capacitor, and to then measure the rate at which the voltage in the capacitor changes. With a known input, this process can be used to determine the capacitance of relatively large capacitors with a small test current. An alternating current at a steady voltage can be used for test purposes as well.
Capacitors are manufactured in a wide variety of sizes. Large models used in power transmission can contain many orders of magnitude more electrical power than the extremely tiny capacitors built into modern integrated circuits. The range of capacitor sizes means that most types of capacitance meter are optimized for measuring capacitance in capacitors of only certain sizes.
The small test current generated by the capacitance meter function of a standard handheld digital multimeter is not sufficient to generate an accurate reading for a large industrial capacitor. Similarly, this same tiny current might actually be powerful enough to overwhelm the resistor in a tiny capacitor located on a circuit board. Specialized and highly precise models of capacitance meter exist for the measurement of capacitance at this level.