Operation
Theory of Operation
OW-503-4 is designed to switch power to devices under test, or to the Signal Midplane power rails. Each channel has a 40A,
soware enabled relay. Relay common for all channels is connected to the IN net. Relay normally open is connected to the output
for each channel.
0-55A current sense circuit is based on LEM LAH-25-NP closed loop Hall Eect sensors. The when current flows through the sensor
primary winding, the hall sensors generate a proportional current in the secondary winding to cancel out the flux in the core. The
cancellation current needed is governed by the turns ratio of the primary (input) and secondary (output) windings, much like a
transformer. A resistor converts the output current to an output voltage, and a selectable set of parallel capacitors provide low
pass filtering of this signal.
Output Voltage is calculated by: , where = 182, = 1000.Vo=Ns
R I
o o RoNs
Caution: Sensor output voltage must stay in balance with the input current! . The board power supply is limited to182IV o= . o
±10V. If the output reaches 10V, the input current must not go any higher than 55A or the sensor cores may become permanently
magnetized and the sensors will need recalibration. Note that when the sensor is o, no secondary cancelling current will flow,
and the core will be magnetized by any input current. The switch protects the sensor when power is o.
Each channel has a 10Ω 0.1% soware selectable shunt to measure current when the DUT is in sleep or power-down mode. The
dierential signal from the shunt runs directly out the back of the chassis, where it can be sensed by a fully dierential ADC or
voltmeter. Because is is sensing power directly, the adc or voltmeter must be galvanically isolated. When not enabled, the shunt is
bypassed.
Configuration
11
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