Keysight 8478B, Руководство по эксплуатации и обслуживанию

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20 Keysight 8478B Thermistor Mount
Operation
Zero Set
2-
Zero Set
It is necessary to electrically zero-set the Power Meter before making a power
measurement. To preserve the same zero reference through the measurement,
maintain the same thermal environment when RF power is applied.
Recommended setups for 430 and 431 zero-settings are presented in
“Unbalanced Operation with Model 431A/B/C and 430 Power Meters” and
“Balanced Operation with Model 431C Power Meter” . The recommended
setup for zero-set in the 432 is shown in “8478B/432” .
RF Power Turned Off for Zero-Set
There is minimum zero drift when the zero is set with the RF system connected
to the thermistor mount and the RF power switch off or greatly attenuated by
the generator attenuator. After allowing time for the mount to stabilize
thoroughly, follow zero-set procedures in the Power Meter manual.
Unbalanced Operation with Model 431A/B/C and 430 Power Meters
When the RF source presents a high 10kHz output impedance of 100k ohms or
greater, the power meter may be zeroed with the 8478B disconnected from the
RF source and unterminated as explained in the previous section. If the RF
source presents a low 10kHz impedance of 1k ohm or less, a zero setting made
with the 8478B disconnected from the RF source and unterminated will not be
the proper zero setting for power measurement. This error can be eliminated by
terminating the 8478B in an impedance that approximates the RF source
impedance at 10kHz while zeroing the power meter. For example, if the RF
source 10kHz impedance is 50 ohms, terminate the RF input connection to the
8478B with a 50 ohm resistor.
Balanced Operation with Model 431C Power Meter
When using a balanced mount, if it is inconvenient to turn off RF power in the
RF source, connect the 8478B to the RF source and set 431C Power Meter
RANGE switch to obtain an approximate midscale reading. When the reading
does not drift, disconnect the 8478B from the source, zero the power meter,
and immediately reconnect the mount to the RF source for the power
measurement.
8478B/432
When it is inconvenient to turn the RF power off while using the 8478B/ 432
combination simply remove the mount from the source, and using the COARSE
and FINE ZERO, zero the 432.