Front Panel Operation
Publication 31470-001, Rev C, November 2, 2017
2-41
2.4.17
Optimizing Measurement Speed
In many power measurement situations, measurement speed is defined in terms of settling time following a
step change in average power. In other words, it is desired to know the average power level within some
specified tolerance as quickly as possible following a power level change. This is often accomplished by setting
up the power meter in free-run mode remotely and monitoring the collected measurement data with the host
computer until it falls within the predetermined tolerance window.
The Auto average feature of the 8650B eliminates the need for the host computer to do any data monitoring
and can be set up to automatically output measurement data when it has settled to within the specified
tolerance. This is done over GPIB by triggering each measurement with a TR2 command and waiting for the
meter to signal the host with an SRQ. The SRQ is asserted and the data is put on the bus as soon as the power
measurement has averaged long enough to be within the specified tolerance.
The tolerance is specified by including the measurement settling tolerance parameter with an FA command
(Auto average on). This parameter is specified in terms of percentage. For example, if a measurement settling
tolerance of 1% is specified, the 8650B Auto average algorithm will specify an averaging time just long enough
so that the result put on the bus is within ±0.5% (that is, ±0.02 dB) of the average power. Thus, the settled
measurement data is available on the bus in the minimum time necessary to be within the specified tolerance.
The tolerance specified in the FA command is a
target
tolerance. For example, it is possible that the peak-to-
peak power variation of the signal being measured is so great that the maximum averaging time of 20 seconds is
not long enough to reduce the variation to within the specified tolerance. It is also possible that the rate of
power variation is so slow that more than 20 seconds of averaging is required. In these cases, further averaging
would have to be done by the host computer.
The following HTBasic™ format (HTBasic is a trademark of TransEra Corporation) example program shows how
to set up a triggered measurement over GPIB, optimized for speed using the auto averaging feature:
Tr2:
! Read using TR2 command
ON INTR 7 GOSUB Srq_interrupt
! Set up SRQ interrupt
ENABLE INTR 7
! Enable SRQ interrupt
OUTPUT 713;*SRE41
! Set service request mask
OUTPUT 713;CS
! Clear status byte
OUTPUT 713;TR2
! Trigger measurement
Data_ready=0
! Clear flag
WHILE Data_ready=0
! Wait for data ready
END WHILE
RETURN
Srq_interrupt:
! SRQ jumps here
State=SPOLL(713)
! Get status byte
IF BIT(State,0) THEN
! If the Data Ready bit is set...
Data_ready=1
! Set the flag
ENTER 713;Tr2_reading
! Read the measurement
OUTPUT 713;CS
! Clear the status byte
OUTPUT 713;*SRE0
! Clear the service request mask
END IF
RETURN
Содержание 8650B Series
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