Boonton 4530 Peak Power Meter User Manual - Manual (Page 71)

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Boonton Electronics Chapter 3
4530 Series RF Power Meter Operation
3.13 RECORDER OUTPUT CALIBRATION
The recorder output may be user calibrated for maximum in-system accuracy when used as a measurement monitor. The
output span of the hardware is -10.0 to +10.0 volts. This span is covered by a 12-bit D/A converter, which generates
4096 voltage steps to cover the 20 volt span, or about 5 millivolts per step. The absolute accuracy specification is
about 100 millivolts at any point on the transfer function, which may be further degraded by loading of the output.
However, the zero offset and gain may be adjusted by the user to provide better absolute accuracy stand-alone and in
system. After calibration, an absolute accuracy of 20mV at all points should be easily achievable. It should be noted,
however, that calibration of the gain and offset does not change the minimum and maximum voltages that are gener-
ated, only the transfer function in between. The minimum and maximum voltages are determined by hardware toler-
ances, and are still subject to the 100 millivolt absolute accuracy specification.
The procedure to adjust the recorder output consists of setting the recorder output voltage level to two different
values, recording the voltage, and adjusting offset and slope to achieve the desired readings. From the front panel, the
following menu commands are used for the calibration. See the section 3.11.8 for detailed descriptions of these menu
commands.
Utilities > Recorder > Force (sets voltage)
Utilities > Recorder > Calibrate > Zero Adj (adjusts offset)
Utilities > Recorder > Calibrate > Slope Adj (adjusts slope, or gain)
Utilities > Recorder > Calibrate > Save Cal (saves the adjustment to nonvolatile calibration memory)
If performing the calibration from the remote interface, the bus commands should be substituted for the menu com-
mands. See section 4.5.17 for detailed descriptions of these remote commands.
OUTPut:RECOrder:FORCE
OUTPut:RECOrder:CALibration:ZERO
OUTPut:RECOrder:CALibration:SLOPe
OUTPut:RECOrder:CALibration:SAVE
To perform the recorder output calibration, the following steps should be followed:
1. Connect a precision, high-impedance (10M or greater) DVM to the recorder output, with the recorder also con-
nected to your monitoring system, if desired.
2. Force voltage to 0.000 volts using the Force command, and record the DVM reading. Other voltages may be used,
if desired.
3. Use the Zero Adj command to adjust the zero offset, and achieve a reading as close to the force setting (normally
0.000 volts) as possible, typically within 3mV. Use the
∧∧∧∧∧ ∨∨∨∨
∧∧∧∧ ∨∨∨∨
and
∨
keys to adjust the value up or down, then press
Enter/Run to update the voltage. The zero offset may be adjusted up or down by 1.000 volt, corresponding to
approximately 10% of the range. If the DVM reading is positive, the zero offset setting should be decreased by
approximately that same value. For example, if the reading is 27.2mV, and the current Zero Adj setting is 0.004 volts,
the new setting should be: 4.0mV - 27.2mV = -23.2mV = -0.023 volts. Note that the output voltage resolution is only
5mV, so not all setting changes will result in a change in the output voltage.
4. Force the voltage to 9.000 volts using the Force command, and record the DVM reading. Other voltages may be
used, if desired.
5. Use the Slope Adj command to adjust the slope, or gain of the output., and achieve a reading as close to the force
setting (normally 9.000 volts) as possible, typically within 3mV. Use the
∧ and ∨
keys to adjust the value up or
down, then press Enter/Run to update the voltage. The slope is stored adjusted as a “delta percent” from the
default slope, and may be adjusted up or down by 10% (corresponding to 90% to 110% of default). If the DVM
reading is positive, the slope setting should be decreased by an appropriate amount. For example, if the reading
is 9.260 volts, and the current Slope Adj setting is 1.61%, the slope is too high by: ((9.260 / 9.000) - 1) x 100 = 2.89%.
This means the new slope setting should be 1.61 - 2.89 = -1.28%. Note that the output voltage resolution is only
5mV, so not all setting changes will result in a change in the output voltage.