Ancillary Functions - Agilent Technologies E4416A Service Manual

Theory of Operation 4

Ancillary Functions

The measurement assembly also measures the sensor resistor voltage to detect
whether a power sensor is present. If a power sensor is connected (or
disconnected) an interrupt to the A2 processor assembly is generated.
Circuitry on the board is then used by the processor to determine the sensor
model, and whether it's connected to the front or rear panel. The processor
then configures the board's ancillary functions, such as chop frequency, chop
voltage levels and also programmes the DSP with the appropriate code for that
sensor type. If the sensor was one of the E- Series then the processor reads
calibration data from the sensor's E2PROM using the I2C bus. The processor
then uses the board's auxiliary ADC (XADC) to measure the sensor
temperature which is used in conjunction with the calibration data to provide
temperature corrected power measurements.
This assembly produces the differential drive signal for the power sensor's
chopper. The processor assembly programs the level and frequency of these
signals:
• For 848x Series power sensors, this signal is 0 V and − 10 V at 217 Hz.
• For E- Series power sensors, this signal is +7 V and − 3 V at 434 Hz.
The XADC is also used to support system built in test by being capable of
digitizing a signal routed to it from the processor assembly.
As described earlier the E- Series power sensors have built in serial EEPROM
and range switching which is controlled or accessed via the measurement
assembly. The N- chop sensor wire used by the 848x Series power sensors
doubles as a serial clock and the sensor resistor line doubles as a
bi- directional serial data line. The wire labelled "Auto Zero" is also used as a
serial bus enable control.
The auto zero line is grounded to the sensor ground line when an 848x Series
power sensor is used. Autozeroing is accomplished without the need for this
signal in the power meter.
All clocks are derived from the 20 MHz system clock that is generated on the
A2 processor assembly and distributed on the A5 daughter assembly.
The E9320 sensors are provided with switchable power supplies.
E4416A/E4417A Power Meters Service Guide 85
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