Boonton 4540 Peak Power Meter User Manual - Manual (Page 51)

Boonton 4540 Series RF Power Meter
Operation 4-3
4.4 Sensor Calibration
The Model 4540 Series features a built-in AutoCal process that automatically calibrates the Peak Power sensors for all
measurement modes, and also calibrates most CW Power sensors for the modulated measurement mode. An internal
programmable 50 MHz calibrator outputs discrete incremental power levels covering the dynamic range of the sensor.
Zeroing is part of the AutoCal process and is adjusted for the High and Low video bandwidths where applicable.
A Fixed Cal automatic calibration process is also provided that can be used with any CW Power sensor, but is intended for
those that cannot be calibrated by the AutoCal process. The internal programmable 50 MHz calibrator provides a single, fixed
level output signal at 0, +10 or +20 dBm as required. Zeroing is also a part of this process.
No calibration is needed for Voltage Probe sensors, but Zeroing is required. This is a single step process with no input signal
applied.
An external programmable 1 GHz calibrator accesory, Model 2530, is also available. When connected to the 4540 Series, the
external 1 GHz calibrator can be controlled by the 4540's menus just as the internal calibrator. This allows Peak Power
sensors and CW sensors to be calibrated at 1 GHz. Fast, single-bandwidth Peak Power sensors cannot be calibrated at 50
MHz. See Appendix B for information and specifications.
Note
You must calibrate the channel 1 sensor using the AutoCal or Fixed Cal routine whenever the Priority
Message field reads ―CH 1 Needs AutoCal‖; and, similarly, the channel 2 sensor when the message ―CH 2
Needs AutoCal‖ appears. If a sensor is to be used in both channels, a calibration is required for each.
During the power-on initialization, the instrument checks its calibration files and restores channel and
sensor calibration data previously stored. Measurements using a particular channel and sensor cannot be
performed unless a valid set of calibration data is present.
Before beginning calibration a warm-up period may be required. If the instrument has not been "On" for at leat 15 minutes, a
15 minute warm-up period is required before the sensors can be calibrated to full accuracy. If the sensor to be calibrated has
not been connected for at least 15 minutes with the instrument "On", a 15 minute warm up period is required.
To initiate AutoCal, Fixed Cal or Zero, press the CAL function key to open the Calibration menu. If the top 3 boxes of the
menu are not in the channel color (yellow=Ch1, blue=Ch2) you desire, press the CAL key again to obtain the alternate
channel. Then press the Autocal, Fixed Cal or Zero menu key. A popup will appear to indicate the status of the selected
process. If you have installed the optional model 2530, 1GHz calibrator, you can select it or the internal 50 MHz calibrator
with the Sel Calibrator menu key.
Alternatively, you can press the Menu function key and the Channel > Channel 1 | 2 > Calibration menu path to the same
menu.
If necessary, you can abort AutoCal, Fixed Cal or Zero by pressing the ESC key. This will restore the calibration status that
existed before the process was started. Calibration accuracy varies with signal power, as described in Subsection 1.6
Specifications. An analysis of calibration accuracy is presented in Section 6.0 Application Notes.