Test Equipment

Troubleshooting computers
Troubleshooting tools
Test Equipment

Multi-meters
This is a piece of test equipment that is used by most IT Systems Support persons. It can usually take reading of voltages, both AC and DC, current, again both AC and DC, and sometimes resistance values in ohms.
There are broadly two different types:

The basic principles of using them are very much the same.
To perform a measurement, the multi-meter is first switched into the appropriate mode - generally done by moving a rotating dial to point to the desired unit of measurement and/or a separate switch selection.

Over-Voltage/Current Protection
Some meters have a feature known as over-range protection. One common problem in taking measurements is that often the value to be measured is unknown, and the wrong unit might be selected.
For instance, if a full scale setting of 12 volts, but the actual voltage in the circuit was 200 volts, then clearly the meter will suffer considerable damage.
The safest method is to start at the highest setting and slowly work down until the correct range setting is reached. In general, for an analogue meter, the needle position when taking the measurement should be about 50-75% of the maximum reading, to obtain the greatest accuracy.
Over-range protection is additional circuitry within the meter, to protect it in the event of an inappropriately low range being selected. This feature is NOT on all meters.

Auto-ranging
This is the ability of the meter to automatically select the correct range when a measurement is taken. This feature is provided with the more expensive digital meters.

Temperature probes
Many of the more expensive multi-meters will have an additional facility for measuring temperature. There are occasions when a fault, particularly an intermittent one, will be temperature-related, and it is useful to be able measure the ambient temperature inside the equipment casing. This can be done by inserting a temperature probe (usually a thermistor.) into the casing and reading the temperature value on a scale on the multi-meter. Dedicated electrical thermometers are also available.

Insulation Testers
Housed in similar casings to the multi-meters, these instruments are capable of inflicting severe damage to electronic equipment and must be used with extreme care. Their purpose is to measure the resistance of cable insulation in MW. To do this accurately, it is necessary to use much higher test voltages than those used by multi-meters. Generally this value is between 250 and 1000vdc, generated using a battery operated voltage multiplying circuit housed within the instrument casing.
Safety precautions are essential when using this equipment:

Time Domain Reflectometer (TDR)
This sophisticated piece of test equipment is designed for quick and accurate fault location in the signal transmission cables such as co-ax and twisted pair, commonly used in computer networks. Using the TDR requires some training and practice but a competent operator can quickly locate even the most obscure cable fault.

The TDR operates by sending a signal pulse of between about 2 nanoseconds and 2 microseconds duration along the cable. All or part of the signal will be reflected back to the TDR, and the time it arrives back will be used to measure accurately the distance to the fault (very useful if the cable is buried). The pattern of the return pulse will indicate the type of fault - short, high resistance etc. It can even indicate an unauthorised connection, such as a phone tap, etc. The important thing to remember is that the signal used in the test is comparable to the signal normally on the cable, and the faults are located by measuring impedance changes in the cable. Many of these cable faults would not show up using conventional continuity testers.
TDRs are also available for fibre-optic cables.
TDRs can be very expensive, but hand-held pocket sized versions are available for less than £500.