Image Credit: Krytar, Inc. | E-Z-HOOK | Extech Instruments, A FLIR Company | Hoyt Electrical Instrument Works, Inc.
Electrical test probes are used to establish a connection between a circuit under test and the measuring instrument. There are several basic types of products. Voltage probes are used to measure voltage. Current probes are used to measure current. Oscilloscope probes have a specified operating bandwidth and, in some cases, built-in switchable attenuators. Differential probes are used to measure differential signals which are referenced to each other instead of ground. By contrast, single-ended test probes are electrical test probes used to measure signals referenced to ground. Logic probes are used to measure logic levels in digital circuits. Semiconductor probes and high-density probes are fine point, spring loaded probes that are usually mounted in a test jig. These electrical test probes are used to test semiconductor interconnects and high-density circuit boards.
Different Types of Probes
Other types of electrical test probes include coaxial probes, polarity probes, continuity probes, high frequency probes, high voltage probes, magnetic probes, and optical probes. A coaxial test probe is a spring loaded, signal-conducting probe insulated from its shell or shielding tube by a dielectric material. Coaxial test probes have rated nominal impedance similar to a coaxial cable. A polarity probe automatically determines the polarity of the circuit under test. A continuity probe is used to test circuit conditions for continuous connection. Typically, continuity test probes are bundled with a continuity tester. A high voltage probe is used to measure high voltage signals. Magnetic probes sense magnetic fields in solenoid-operated devices, stepper switches, relays, valves and coils. Optical probes are electrical test probes that convert optical signals into electrical signals for convenient analysis of oscilloscopes and other devices.
How to Select the Right Probe
Selecting electrical test probes requires an analysis of performance specifications. The attenuation factor is the amount by which the electrical test probe reduces the amplitude of the signal being measured. This extends the measurement range for an instrument such as an oscilloscope. For instance, a 10X probe reduces the measured signal to 0.1 of its amplitude, allowing the test instrument to measure signals ten times larger than what its maximum range allows. Choices typically include 1X, 10X, 100X, 500X, and 1000X.
There are many different configurations for electrical test probes. An alligator clip electrical test probe has a spring-loaded jaw with serrated teeth that grip the point being measured. A bent metal electrical test probe has bent metal contacts, relatively fine pieces of metal that are formed into a curvilinear shape in order to provide a cantilever effect. Normally, the metal contacts are then insert-molded or stuffed into a nonconductive carrier. A portion of the metal contact protrudes beneath the carrier for attachment to a printed circuit board (PCB) by surface mount or through-hole interconnection. A board or chip configuration has a specialized probe tip that is used to examine signals on PCBs and integrated circuit (IC) chips. Other configurations include conductive elastomers, extended-fine tip, flat blade, hook, pin-and-socket, pincher, probe card, spade lug, spring loaded, and wireless.
ASTM B667 - STANDARD PRACTICE FOR CONSTRUCTION AND USE OF A PROBE FOR MEASURING ELECTRICAL CONTACT RESISTANCE
UL 61010B-2-031 - ELECTRICAL EQUPMENT FOR MEASUREMENT, CONTROL, AND LABORATORY USE; PART 2: PARTICULAR REQUIREMENTS FOR HAND-HELD PROBE ASSEMBLIES FOR ELECTRICAL MEASUREMENT AND TEST
IEC 61010-031 - SAFETY REQUIREMENTS FOR ELECTRICAL EQUIPMENT FOR MEASUREMENT, CONTROL AND LABORATORY USE - PART 031: SAFETY REQUIREMENTS FOR HAND-HELD PROBE ASSEMBLIES FOR ELECTRICAL MEASUREMENT AND TEST