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This test report presents the data and describes the procedures for testing the current-carrying capacity for QA's test probes. This information is useful for test and design engineers when calculating probe requirements for high current and temperature applications.

Measure the current capacity of test probes. Two types of tests were performed; both were simulations of common applications for probes. The first tested a solitary probe mounted in a G10 fixture plate, while the second tested a group of probes (3x3 grid pattern).

Dimensions are in in. [mm]

The current-carrying ability of a probe is measured with respect to probe temperature. The upper temperature limit of a spring probe is determined by the spring material. Springs which are made of music wire can be used without adverse effects up to 250° Fahrenheit [120° C]. Although stainless steel springs are also used in QA probes and can withstand temperatures up to 400° F [204° C], 250° F [120° C] is used for the upper temperature limit since the probe user may not always be certain of the spring material.

A controllable DC current source was used to provide a constant current through the probe and socket assembly being tested, while a thermocouple was used to track the temperature of the probe. The current was increased in one Ampere intervals (one-half intervals for the 039-16 and 025-16 Series), and sufficient time was allowed between increases for the temperature to stabilize. As current increased, probe temperature increased, and testing continued until the 250° [120°C] Fahrenheit threshold was reached.

For the first test, a solitary probe was oriented as shown in the sketch below. A probe from each series was mounted in a 5/16" block made of G10. The block stood horizontally on four legs, and airflow was blocked by baffles arranged around the test block.

Setup for measuring current versus temperature for a single probe/socket assembly.

Wires for supplying current to the probe were 20 AWG or greater. One current supply wire was connected directly to the tail of the socket. The other was connected to a solder-coated plate which was in contact with the probe tip. This contact plate was mounted such that the probe was compressed to its rated 2/3 stroke. The test set up was intended to closely simulate typical applications for test probes.

The second test (probe groups, 3x3 Grid), nine probes and sockets were mounted on a three-by-three grid of the appropriate center spacing. All nine probes were wired in series by connecting the appropriate socket tails, and by selectively jumping the tips in succession with a solder-coated plate simulating a typical printed circuit board. In this way, the same current was assured to run through all nine probes. The thermocouple was connected to the center socket at the same location as in the previous test.

The plotted graphs compare the temperature versus current for all of the probe series. The sockets used for each series are listed in the table, the 100-25 Series were all tested in 100-SDN250S sockets with exception to the 100-PRH2509S probes which were tested in 100-SDH250W sockets and plotted on the 100-25 Series graphs. Additional tests included the testing of the various spring forces and varying the stroke lengths for the 100-25 Series. Complete numeric test results are available.

• As the group data shows, higher probe densities decrease the probes current carrying ability. This is due to the combined heat generated by the probes and the decrease of air circulation via natural convection. Because each application is unique, it is recommended that appropriate tests be conducted before probes are put into service in applications with high currents, high probe densities or limited airflow.

• These temperature measurements were made in the absence of any forced convection. Providing airflow (by means of a fan, for example) around the sockets will reduce the temperature for a given current. Also, tests have shown that the airflow present due to leaks in a typical vacuum fixture will reduce temperature.

• For conditions where the ambient temperature differs from the 75° F [24° C] ambient of these tests; shift the data by the same amount that the ambients differ to determine whether the 250° F [120° C] limit is exceeded. For example, a 100-25 series probe with a P tube operating in an environment with an ambient temperature of 120° F [49° C] will exceed 250° F [120° C] at 7 Amps (instead of 14 Amps at 75° F [24° C] ambient).

• Differences in current carrying capacity for various springs are not significant.

• Differences in current carrying capacity for various strokes are not significant.

• Note that although the probe will not be damaged from operation at temperatures up to 250° F [120° C], some types of plastics used as mounting plates will not withstand this temperature. Also, the operator must be protected against contacting probes at high temperatures.

• This data reflects performance at 100% duty cycle. Higher currents can be carried for pulses of short duration. For simplicity, apply higher currents for no longer than one second (longer pulses may be carried, but require that thermal inertia and rate of temperature gain be known). For example, the electrical resistance of 100-PRH2509S in 100-SDH250W averages 7 milliohms and carries a maximum current of 20A; it is able to continuously dissipate a maximum of 2.8W (P=I2R). At 50A, it would dissipate about 17.5W, which means the duty cycle must be reduced to 16%. So, to avoid overheating this probe at 50A, power must be applied for no more than 160 milliseconds (1 second x 16%).

• For comparison, note that a Kynar-insulated solid copper wire the same diameter as a 100-25 Series probe tube (.054 [1.371]) reaches 250° F [120° C] at 29A.

025-PRP1641S	039-PRP1614S-S	050-PLP0513S	050-PLP1609S	050-PTP2509S
050-PRP2509S	Single Probe	Multiple Probes 3x3 Grid	Single Probe	Multiple Probes 3x3 Grid
Single Probe	Multiple Probes 3x3 Grid	Single Probe	Multiple Probes 3x3 Grid	Single Probe
Multiple Probes 3x3 Grid	Single Probe	Multiple Probes 3x3 Grid	Single Probe	Multiple Probes 3x3 Grid
Single Probe 100-PRP2509 L, S, H, Y & X Springs	Multiple Probes 3x3 Grid 100-PRP2509 L, S, H, Y & X Springs	Single Probe Variable Stroke Lengths 100-PRP2509S	Multiple Probes 3x3 Grid Variable Stroke Lengths 100-PRP2509S