Agilent Technologies 3458A User Manual

92 Chapter 4 Making Measurements
Reading Formats
This section discusses the ASCII, single integer (SINT), double integer
(DINT). single real (SREAL), and double real (DREAL) formats that can be
used for storing readings or for outputting readings on the GPIB. Storing
readings in memory is described later in this chapter under "Using Reading
Memory"; outputting readings on the GPIB is discussed later in this chapter
under "Sending Readings Across the Bus".
ASCII The ASCII format is 15 bytes per reading encoded in scientific notation in
standard units of volts, amps, ohms, hertz, or seconds as follows:
SD.DDDDDDDDESDD
Where:
S = sign (+ or -)
D = 0-9
E = delimiter between mantissa and base 10 exponent
Single and Double
Integer
The single integer (SINT) format has 2 bytes per reading and the double
integer (DINT) format has 4 bytes per reading. Both formats use two's
complement coding.
Note When using the SINT or DINT memory/output format, the multimeter
applies a scale factor to the readings. The scale factor is based on the
multimeter’s measurements function, range, A/D converter setup, and
enabled math operations. You should not use the SINT or DINT format for
frequency or period measurements; when a real-time or post-process math
operation is enabled (except STAT or PFAIL); or when autorange is
enabled.
Two's Complement
Binary Coding
Two's complement binary coding is a method that allows a binary number
to represent both positive and negative integers. Two's complement coding
is done by changing the sign and, in effect, the decimal equivalent of the most
significant bit (MSB). When the MSB is set (1), in a 1 byte two's complement
number, its value is 1
´ -(2
7
) = -128. When the MSB is reset (0), its value is
0
´ -(2
7
) = 0. Note that the range of an 8 bit, 1 byte two's complement number
is -128 to 127, not 0 to 255.
The following example resolves the decimal equivalent of this two's
complement word:
10110101 10010110
This two's complement word is equivalent to:
–(2
15
) + 2
13
+ 2
12
+ 2
10
+ 2
8
+ 2
7
+ 2
4
+ 2
2
+ 2
1
Which evaluates to: –19050

Agilent Technologies 3458A Specifications

General

Model	3458A
Manufacturer	Agilent Technologies
Category	Multimeter
Digits	8.5
Sampling Rate	100, 000 readings/second
Interface	GPIB

Summary

Safety Symbols and Warnings

General Safety Precautions (WARNINGS)

Outlines essential safety precautions for operating, servicing, and repairing the product to prevent injury or damage.

Chapter 2 Getting Started

Operating from the Front Panel

Covers using front panel keys, making measurements, changing functions, and controlling display settings.

Operating from Remote

Explains how to control the multimeter remotely via GPIB, including address management and command sending.

Chapter 3 Configuring for Measurements

General Configuration

Configuring for DC or Resistance Measurements

Details how to configure the multimeter for DC voltage, DC current, and 2-wire or 4-wire resistance measurements.

Configuring for AC Measurements

Explains how to configure the multimeter for AC voltage, AC current, frequency, or period measurements.

Chapter 4 Making Measurements

Triggering Measurements

Explains the three-event triggering hierarchy (arm, trigger, sample) and various event choices.

Using Reading Memory

Sending Readings Across the Bus

Increasing the Reading Rate

Discusses the multimeter's high-speed mode and factors affecting reading rate and transfer speed.

Math Operations

Explains real-time and post-process math operations, enabling/disabling them, and math registers.

Chapter 5 Digitizing

Digitizing Methods

Details DCV, Direct-Sampling, and Sub-sampling methods, summarizing their characteristics and signal paths.

The Sampling Rate

Level Triggering

Describes how to specify voltage and slope for sampling initiation, with examples for DCV and direct-sampling.

DCV Digitizing

Direct-Sampling

Explains direct-sampling using track-and-hold, its bandwidth, and specifying ranges via max._input parameter.

Sub-Sampling

Covers sub-sampling fundamentals, advantages, and how to specify effective interval and number of samples.

Chapter 6 Command Reference

ACAL

Instructs the multimeter to perform self-calibrations (ALL, DCV, AC, OHMS) and discusses autocalibration security.

NRDGS

OFORMAT

PRESET

Configures the multimeter to one of three predefined states: NORM, FAST, or DIG for different operation modes.

SUB

Stores a series of commands as a subprogram, assigning a name for later execution.

TARM

Defines the trigger arm event to enable the trigger event and can be used for multiple measurement cycles.

TEST

Causes the multimeter to perform a series of internal self-tests to check hardware and software integrity.

TRIG

Specifies the trigger event that initiates a measurement, working with TARM and NRDGS.

Chapter 7 BASIC Language for the 3458A

BASIC Language Commands

Subprograms

Explains how to store, execute, and manage BASIC language subprograms for system control and automation.

Appendix B GPIB Commands

TRIGGER (GET)

Appendix C Procedure to Lock Out Front/Rear Terminals and Guard Terminal Switches

Procedure

Outlines the steps for installing the switch lockout kit, including covers and pushrod removal.

Appendix D Optimizing Throughout and Reading Rate

Maximizing the Testing Speed

Covers strategies like tailoring communication paths, program memory, and state storage for optimal testing speed.

DC Volts, DC Current and Resistance

Explains the measurement paths (DCV, track-and-hold) and trade-offs for DC measurements.

AC Volts and AC Current

Details the three ACV measurement techniques (Analog, Synchronous, Random) and their trade-offs.

Frequency and Period

Optimizing the Testing Process Through Task Allocation

Discusses allocating tasks between the DMM and computer using math functions, memory, and program structure.

Math Operations

State Storage and Program Memory

A Benchmark

Appendix E High Resolution Digitizing With the 3458A

Speed with Resolution

Details the multimeter's flexibility in speed and resolution for audio frequency bandwidth.

Digitizing Analog Signals

Avoiding Aliasing

Provides methods to avoid signal distortion caused by aliasing, ensuring accurate waveform representation.

Choice of Two Measurement Paths

Describes the standard DCV path and the track-and-hold path for digitizing and sampling.

Capturing the Data

High Speed Data Transfers

Errors in Measurements