ANSI STM11.13:2018 pdf free download – Two-Point Resistance Measurement
5.0 GENERAL DISCUSSION
This method is recommended for testing items with irregularly shaped surfaces, and small and narrow surfaces. Conventional concentric ring and parallel bar electrode configurations are used for testing planar items only. However, most packaging items are not planar. Examples include shipping tubes, trays, tote boxes and carrier tapes. The probe described in this standard test method employs springs to apply consistent contact pressure between the electrode and the item. Force created by springs is subject to variance from wear, contamination and manufacturing tolerance. This variance is acceptable for this application. Elastomeric electrodes compensate for uneven item surfaces yielding consistent results between laboratories and test operators.
6.0 TEST EQUIPMENT
6.1 Two-Point Probe Refer to Figure 1 and Table 1 . This two-point probe consists of an insulated metal body with a Teflon Ò insulator inserted into each end. One insulator holds test leads; the other holds receptacles that accept spring-loaded pins. One receptacle is surrounded by a cylindrical insulator, which is surrounded by a metal shield. The pins are gold plated and have a spring force of 0.465 kg (1 6.4 ounces) + 1 0% at a travel of 4.32 mm (0.1 7 inch). The pin tips are machined to accept friction fitted 3.1 80 mm (0.1 25 inch) diameter electrically conductive rubber electrodes. The rubber has a Shore-A (IRHD) durometer hardness of 50-70 (ASTM Method D 2240). The electrodes are 3.1 80 mm (0.1 25 inch) long. Electrode volume resistivity is < 500 ohms-cm.
6.5 Verification Resistors
The low resistance verification fixture will consist of a 1 .0 x 1 0 4 ohm (+ 1 %) resistor electrically bonded to two isolated metal contact plates. The plates must be of size and shape so that each probe electrode contacts only one plate. The plates shall be affixed to a material with the same properties as the insulative support surface described in Section 6.2. Figure 3 illustrates one possible configuration of a resistance verification fixture. The high resistance verification fixture will consist of a 1 .0 x 1 0 1 1 ohm (+ 5%) resistor electrically bonded to two isolated metal contact plates. The plates must be of size and shape so that each probe electrode contacts only one plate. The plates shall be affixed to a material with the same properties as the insulative support surface described in Section 6.2. Figure 3 illustrates one possible configuration of a resistance verification fixture. The actual value of the resistors should be measured periodically in accordance with the manufacturer’s recommendation. This measured value should be used to verify probe operation.
8.0 VERIFICATION PROCEDURE
a) Correct probe operation shall be verified by measuring known resistance values.
b) Connect the probe to the meter as shown in Figure 2.
c) Place the probe electrodes onto the low resistance verification fixture as shown in Figure 3.
d) Compress the spring-loaded pins downward approximately half of the length of travel (Figure 4).
e) Apply 1 0 volts for 1 5 seconds and observe the resistance.
f) Record the resistance value. The value should be within 1 0% of the actual resistor value. If it is not, do not use the probe.
NOTE: If the result is not within 1 0% of the actual resistor value, refer to the manufacturer’s trouble shooting procedures.
g) Repeat the procedure using the high resistance verification fixture at 1 00 volts.