12
to the constant transfer interruption. Also, the amount of data gathered will quickly
become unmanageable. The LCTS is a life cycle tester and is not intended for
continuous data collection.
Test Circuitry
A simplified diagram of the contact measurement circuitry is shown in figure 6. The
contact is measured using a precision 1.00 KOhm pullup resistor to a 5 volt power
source. The switch contact is arranged between this resistor and ground. A 10-bit
analog to digital converter is used to measure the voltage across the switch contacts.
This type of measurement yields a nonlinear voltage verses resistance characteristic.
This approach has advantages and disadvantages. Advanced calculations must be
performed to generate the equivalent resistance from the measured voltage, but this is
easily accomplished by the PC running the application software. The Model 933A never
needs to make this calculation. The real advantage of this test technique is the
resolution enhancement that it provides on the low end of the resistance range. The
scale is compressed downward. This provides a greater resolution to the “closed” circuit
condition while also yielding an extended dynamic range. The resolution at the top end
of the scale becomes very coarse, but at least very large resistance values can still be
measured.
DUT
1000 Ohms
0.01%
+ 5 Volts
10 Bit
A/D
Reference
Figure 6.
Simplified Contact Measurement Circuitry
Bounce Measurement
The Model 933A measures the electrical contact bounce according to the methods
described in the ASTM Designation F1661 - 96. This testing is optional, and can be
disabled in the failure analysis if not required. It should be noted that the LCTS does not
monitor nor directly control the actuation speed of the device under test. This speed can
