22 NOVEMBER / DECEMBER 2021 Wiring Harness News INDUSTRIAL INFO-TAINMENT

#### Automated Testing for Harnesses ( Part 2 )

By Ray Mumma Cirris Systems ____________________________

# In a previous article on the basics of automated electrical testing we compared manual and automated cable / harness testing . We ’ ll continue that discussion by expanding on one of the topics mentioned , specifically how automated cable / harness testers make measurements . It ’ s a subject that is often overlooked but understanding a few basic concepts can bring more complex issues into better focus .

This is readily accomplished because , while engineers incorporate some amazing tricks under the hood , the fundamental processes are straightforward . These processes can be seen in three basic measurements - continuity , low voltage isolation , and high voltage testing . Let ’ s begin by examining one of the basic formulas in electronics , Ohm ’ s Law , which describes the relationship between voltage ( V ), current ( I ), and resistance

( R ) in a simple circuit with the equation , V = IR .

There are many excellent resources available on the internet describing Ohm ’ s law , so for our purposes , it ’ s adequate to understand the mathematical relationship between the variables . As in all similar equations with three variables , the third can be calculated if the other two are known . Some find the triangle visual helpful as it makes it easy to find the appropriate formula for calculating the unknow by covering its symbol ( Figure 1 ). When doing the math , it ’ s important to remember that the unit of measure for voltage is Volts , for current is Amps , and for resistance is Ohms .

It ’ s also useful to understand that in a simple series DC circuit , the current at any given point is the same as the current at any other point . In the same circuit , the potential difference ( voltage drop ) across an unknown resistance can be measured . In the case of automated cable / harness testers ,

Figure 1 . Ohm ’ s Law