User Manual

Section
4: Operation considerations Model 3760 10-Channel High Current Multiplexer Card
User's Manual
4-2 3760-900-01 Rev. A / July 2017
Reactive loads
The 3760 is specified for resistive loads only. Since reactive loads can cause excessive currents and
voltages, current surge limiting (for capacitive loads) and voltage clamping (for inductive loads) are
required to prevent damaging the relays and external circuitry.
Capacitive loads
The surge current from a capacitive load must be less than 5 A to protect the relays. The next figure
shows typical circuits to limit current surges. Also, consider the maximum load of 100 VA when
determining the current limit. For example, when switching 500 V, the current must be limited to 200
mA (A = 100 VA/500 V) and the limiting resistor calculation of the next figure would be:
R = V/I = 500 V/200 mA = 2.5 kΩ
Use an appropriately rated resistor in the test.
Figure 5: Model 3760 Limiting capacitive reaction (resistor limited)
The Thermistor must have high resistance when cold, low resistance when hot, and have fast
thermal recovery.
Figure 6: Model 3760 Limiting capacitive reaction (thermistor limited)