Bedienungsanleitung Keithley 2001 (Seite 51 von 476) (Englisch)

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Front Panel Operation

2001-900-01 Rev. K/ August 2010 3-19

UNITS

This parameter selects the displayed units for AC voltage

measurements. You can program the ACV units parameter as

follows:

1. From the CONFIGURE ACV menu, select UNITS and

press ENTER. The following menu is displayed:

SET ACV DISP UNITS

VOLTS dB dBm

2. Highlight the desired units and press ENTER.

VOLTS: With volts selected as the units, AC voltage

measurements are expressed in volts.

dB: Expressing AC voltage in dB makes it possible to

compress a large range of measurements into a much smaller

scope. The relationship between dB and voltage is defined

by the following equation:

where:V

is the AC input signal.

REF

is the specified voltage reference level.

The instrument will read 0dB when the reference voltage

level is applied to the input. dB measurements are possible

on all ACV measurement types except positive peak spikes

and negative peak spikes, as these may be negative, and the

log of a negative number is not defined. Note that dB

measurements are specified only for the low frequency RMS

measurement type.

If a relative value is in effect when dB is selected, the value

is converted to dB. If a relative value is stored after dB units

are selected, the units of the relative value are dB.

To set the reference voltage level, perform the following

steps:

1. From the SET ACV DISP UNITS menu, select the dB

option. The following typical message is shown:

dB REF LEV:001.000 V

2. By using the cursor keys ( and ) and the RANGE

 and  keys, you can enter the desired voltage refer-

ence level (0.001V to 750V).

3. Press ENTER to complete the change. If positive peak

spikes or negative peak spikes is the selected AC type,

the change is not allowed.

dBm: dBm is defined as decibels above or below a 1mW

reference. With a user-programmable reference impedance,

the Model 2001 reads 0dBm when the voltage needed to

dissipate 1mW through the reference impedance is applied.

The relationship between dBm, a reference impedance, and

the voltage is defined by the following equation:

where: V

is the AC input signal.

REF

is the specified reference impedance.

NOTE

Do not confuse reference impedance with

input impedance. The input impedance of

the instrument is not modified by the dBm

parameter.

If a relative value is in effect when dBm is selected, the value

is converted to dBm. If a relative value is stored after dB

units are selected, the units of the relative value is dBm.

To set the reference impedance, perform the following steps:

1. From the SET ACV DISP UNITS menu, select the dBm

option. The following menu is shown:

SET dBm REFERENCE

50 75 93 132 300 600

2. Highlight the desired reference impedance and press

ENTER to complete the change. If positive peak spikes

or negative peak spikes is the selected AC type, the

change is not allowed.

dB/dBm notes:

1. dB and dBm units are not allowed with positive or neg-

ative peak spike measurements.

2. dB and dBm units are not allowed with an advanced fil-

ter.

3. With dB or dBm units selected, there is no bar graph on

zero-centered bar graph multiple display.

4. When units are changed from volts to dB or dBm with

A02 and greater firmware, all values less than zero that

depend on the new units are made equal to zero. This in-

cludes, for example, relative values and stored readings.

This avoids the overflow condition of a log of a negative

number.

dB = 20 log

REF

------------

dBm = 10 log

REF



1mW

----------------------------

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