Theory of Operation
A6 Measurement Assembly
The DSP chip controls the logic which sets the chopper driver voltage and frequency control. For the:
•Agilent 8480 series power sensors this is 0 V and -10 V at 217 Hz.
•Agilent E-series power sensors this is +7 V and -3 V at 434 Hz.
The DSP also controls logic to allow the AUX ADC to measure a number of voltages, and when requested, send the relevant data to the host processor. The AUX ADC digitizes a voltage which is produced by the Agilent E-series power sensors and is proportional to temperature. This voltage is required for temperature compensation. This AUX ADC also tests the sensor resistor wires to check sensor continuity. Lastly, use is made of this AUX ADC for the power meter’s self test of both the measurement assembly and the A2 processor assembly. The results are reported back to the A2 processor assembly via the “Internal Serial Bus”.
The Agilent 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 Agilent 8480 series power sensors doubles as a serial clock and the sensor resistor line doubles as a bi-directional serial data line. The “Auto Zero” line is also used as a serial bus enable control.
The wire labelled “Auto Zero” is grounded to the “Sensor Ground” line when an Agilent 8480 series power sensor is used. Autozeroing is accomplished without the need for this signal in the power meter.
All clocks are derived from the 16.67 MHz system clock which is generated on the A2 processor assembly and distributed on the A5 daughter assembly.
Agilent E4418B/E4419B Service Guide | 4-11 |
