user manual
Table Of Contents
- 45 Dual Display Multimeter
- 1. Introduction
- 2. Getting Started
- 3. Operating the Meter From the Front Panel
- 4. Applications
- 5. Operating the Meter Using the Computer Interface
- Introduction
- Preparing the Meter for Operations via the RS-232 Interface
- Preparing the Meter to be Operated via IEEE-488 Interface
- Getting Started With An Installation Test
- How the Meter Processes Input
- How the Meter Processes Output
- Triggering Output
- Service Requests (IEEE-488 Only and Status Registers
- Computer Interface Command Set
- IEEE-488 Capabilities and Common Commands
- Function Commands and Queries
- Function Modifier Commands and Queries
- Range and Measurement Rate Commands and Queries
- Measurement Queries
- Compare Commands and Queries
- Trigger Configuration Commands
- Miscellaneous Commands and Queries
- RS-232 Remote/Local Configurations
- Sample Program Using the RS-232 Computer Interface
- Sample Programs Using the IEEE-488 Computer Interface
- 6. Maintenance
- Appendices
45
Users Manual
3-12
modifier is selected, the relative base is shown in the secondary display. To turn off this
feature, press S and, while holding it down, press K .
dB (Decibels and Audio Power) Modifier
The decibels modifier takes a voltage measurement, converts it to dBm (measure of
decibels relative to one milliwatt), and displays the result on the primary display.
Press I to toggle in and out of the decibels modifier. When the decibels modifier is
selected, "dB" is shown on the primary display.
Decibels can be selected only when a voltage function is selected on the primary display
(volts ac, volts dc, or volts ac + dc). Decibels are always displayed in a single, fixed
range with 0.01 dB resolution. However, the basic measurement itself (e.g. volts ac)
autoranges.
A voltage measurement is converted to dBm using the following formula:
dBm = 10*log (1000*value
2
/reference impedance)
where "value" is the measurement value. The reference impedance can be set to any of 21
reference impedances listed in Table 3-8 by using the list editor as described in "Using
the List Editor" later in Chapter 3.
Table 3-8. Reference Impedances in Ohms
8000 300 93
1200 250 75
1000* 150 50
900 135 16†
800 125 8†
600 124 4†
500 110 2†
* Voltage annunciator lit
† Audio power readings possible
To access the reference impedance list, press S then press I (REF e). The reference
impedance currently selected is displayed, along with the db and e annunciators. Press
U or T to scroll to the desired value, then press E to select a reference impedance
and return the primary display to the measurement function. Press any function (white) or
modifier (light grey) button to exit the reference impedance list without selecting a new
value.
Setting the dB reference resistance to 16, 8, 4, or 2 ohms allows you to use the meter to
calculate audio power. After the reference resistance has been set to 16, 8, 4, or 2 ohms,
press I twice to select the audio power modifier. "POWER" will be shown on the
secondary display.
The following equation is used to make a power calculation:
Audio power = Volts /reference resistance
where volts is the measurement value.