Continuity Test Resistance Calculator

Cable Testers and Harness Testers Made Easy!

Cable Testing Products Support Information Center About Us Contact Us

1-800-441-9910

Continuity Test Resistance Calculator

Use this calculator to help determine effective thresholds for your wire tests. This calculator will help you estimate the maximum resistance of your Device Under Test (DUT), then add in resistance variations from wire length, temperature, diameter, fixturing, and tester accuracy. If you have any questions give us a call at 1-800-441-9910. We'll be happy to "walk you through" an example. In just a few minutes we can explain how to use this calculator.

Step 1) Find the DUT's Maximum Theoretical Wire Resistance

Set the Units of Measure		All lengths in All temperatures in All resistance values in ohms All wire gauges are AWG All wire is copper
Calculate the Resistance of the Ideal DUT (Theoretical)		Wire in DUT:
		Length Gauge (Note 1)	___ ohms
		Contact Mating Resistance (DUT to fixture):
		At Point A: ohms (Note 2)	___ ohms
		At Point B: ohms	___ ohms
	Total Ideal Resistance of DUT (nominal)		___ ohms
Add Variation From Ideal for the DUT		Account for Resistance Increases from:
		Wire Length Tolerance: % (See Note 3)	___ ohms
		Wire Diameters Per Twist Length: (See Note 4)	___ ohms
		Wire Resistance Tolerance: % (See Note 5)	___ ohms
		Temperature Deviation : ° (See Note 6)	___ ohms
		Total (In-Spec) Variance From Ideal	___ ohms
	Estimated Max Resistance of a Good DUT		___ ohms

Step 2) Allow for Real-World Measurement Issues
Option 1 - Four-Wire Add Resistance Variation If Using 4-Wire Measurement		Variance Due to 4-Wire Tester Measurement Error:
		Tester Accuracy for 4-wire Measurement % (of reading)	___ ohms
		Tester Resolution Error ohms	___ ohms
		Total Variation Due to Tester (4-Wire Measurement)	___ ohms
		Resistance From Wear of Mating Contacts ohms (Note 7)	___ ohms
	Estimated Max Measured Resistance of a Good DUT (4-Wire)		___ ohms
Option 2 - Two-Wire Add Resistance Variation If Using 2-Wire Measurement		Variance Due to 2-Wire Tester Measurement Issues: Fixturing wire from tester to:
		Point A: Length Gauge	___ ohms
		Point B: Length Gauge	___ ohms
		Resistance of Fixture Wire (nominal)	___ ohms
		Fixture Wire Variation (diameter/temperature)	___ ohms
		Estimated Max Fixture Resistance	___ ohms
		Tester Accuracy for 2-wire Measurement % (of reading)	___ ohms
		Tester Resolution Error ohms	___ ohms
		Total Variation Due to Tester (2-Wire Measurement)	___ ohms
		Resistance From Wear of Mating Contacts ohms (Note 7)	___ ohms
	Estimated Max Measured Resistance of a Good DUT (2-Wire)		___ ohms
Option 3 - A-620 Specification		A-620 Specification Class III Default Test Requirement	___ ohms

Step 3) Determine the Lowest Practical Test Resistance Threshold
Your "Lowest Practical" Test Threshold Results Summary		We define the "lowest practical test specification" as the lowest resistance setting that passes "in-spec assemblies on in-spec test equipment." If you test at a setting lower than what is practical you will fail assemblies that were manufactured correctly. A DUT with an ideal wire resistance of ___ ohms can have a resistance as high as ___ ohms and be correctly built and in spec. That increase in resistance comes from variations in wire length, conductor diameter, test temperature, and contact resistance. Taking into account the variations caused by test fixturing and tester accuracy the lowest practical test thresholds for that wire are: When testing 2-wire use a threshold higher than ___ ohms. When testing 4-wire use a threshold higher than ___ ohms. The A-620 Class III Default Threshold is ___ ohms.
Notes		(Note 1) Do these calculations on the wire with the highest resistance (smaller diameter wires and longer wires have higher resistances). (Note 2) This is the typical resistance of mated contacts. Get this specification from your connector manufacturer's data sheet. (Resistance will increase with increased mating cycles). (Note 3) This includes both the allowed length tolerance on the DUT's drawing and any pigtail wire length in connectors. (Note 4) Enter the ratio of the insulated wire diameter to length of the twist. If the wires are not twisted then leave the field blank. For example, a twisted pair conductor with an outside diameter (including insulation) of 0.030 inches and a twist length of 0.5 inches per twist has a ratio of 0.5 / 0.030 = 16.7. You would enter 16.7 in the box. (Note 5) The maximum spec for stranded wire is typically 8% higher than then nominal spec for solid copper wire. Some variation from nominal comes from the fact that the diameter of copper strands in the wire will vary from spool to spool. Also, the composition of the copper can vary slightly from lot to lot. Use this field to account for these normal wire resistance variations. A good typical value for stranded wire is 8%. (Note 6) The resistance of the wire is specified at an ambient temperature of 68°F/20°C. If you are testing at a temperature well above that ambient temperature enter the temperature deviation in the box. For example, when testing at 78°F. enter 10°. (Note 7) If the fixturing connectors exceed thier mating cycle life their contact resistance will go up. The higher you set this value the longer you can use a fixturing connector (or connector adapter) before you must replace it. If this value is set too low it will increase fixturing costs, increase failure rates, and slow your production rate.

Updated February 26, 2010. Cirris Systems - Technical Tips - Wire Resistance Calculator