Hewlett-Packard 34401A

Hewlett-Packard

34401A

6.5-digit digital multimeter

multimeter SCPI

Default Address 22

Termination LF

IEEE 488.2 Yes

IDN Patterns

HEWLETT-PACKARD,34401A,*,*AGILENT TECHNOLOGIES,34401A,*,*Agilent Technologies,34401A,*,*

Documentation

The 34401A was one of the most widely deployed bench multimeters in history. Produced from 1991 to 2014, superseded by the 34461A (Truevolt series). Many are still in active lab use. GPIB interface is standard on all units.

Status Byte

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
Operation Complete	RQS/MSS	ESB	MAV	Questionable Data	Error Queue	Unused	Unused
Operation summary bit	Requesting service / Master summary status	Event status byte summary bit	Message available in output buffer	Questionable data summary bit	One or more errors in error queue	Not used	Not used

Use *STB? to read status byte, *SRE to set service request enable register

Commands

IEEE 488.2 Common Commands

Standard IEEE 488.2 commands supported by all compliant instruments

Command	Type	Description
`*IDN?`	query	Identification query — returns manufacturer, model, serial, firmware
Details Returns (string) — Comma-separated identification Example: `HEWLETT-PACKARD,34401A,MY47000001,10-5-2`
`*RST`	command	Reset to factory default state
`*CLS`	command	Clear status registers and error queue
`*ESE {mask}`	command	Set event status enable register
Details Parameters `mask` (numeric) — Bitmask 0-255
`*ESE?`	query	Query event status enable register
Details Returns (numeric) Example: `0`
`*ESR?`	query	Read and clear event status register
Details Returns (numeric) Example: `0`
`*OPC`	command	Set operation complete bit in ESR when all pending operations finish
`*OPC?`	query	Returns 1 when all pending operations complete
Details Returns (numeric) Example: `1`
`*SRE {mask}`	command	Set service request enable register
Details Parameters `mask` (numeric) — Bitmask 0-255
`*SRE?`	query	Query service request enable register
Details Returns (numeric) Example: `0`
`*STB?`	query	Read status byte register
Details Returns (numeric) — Status byte value Example: `0`
`*TST?`	query	Self-test; returns 0 for pass, 1 for fail
Details Returns (numeric) Example: `0` Note: Takes several seconds to complete
`*TRG`	command	Trigger measurement from bus (requires trigger source BUS)

Measurement Configuration

Configure measurement function, range, and resolution

Command	Type	Description
`CONF:VOLT:DC [{range}[,{resolution}]]`	command	Configure for DC voltage measurement
Details Parameters `range` (numeric, optional) — Range in volts (0.1, 1, 10, 100, 1000) or MIN\|MAX\|DEF Default: `DEF` `resolution` (numeric, optional) — Resolution in volts or MIN\|MAX\|DEF Default: `DEF` Example `CONF:VOLT:DC 10,0.001`
`CONF:VOLT:AC [{range}[,{resolution}]]`	command	Configure for AC voltage measurement
Details Parameters `range` (numeric, optional) — Range in volts (0.1, 1, 10, 100, 750) or MIN\|MAX\|DEF `resolution` (numeric, optional) — Resolution or MIN\|MAX\|DEF
`CONF:CURR:DC [{range}[,{resolution}]]`	command	Configure for DC current measurement
Details Parameters `range` (numeric, optional) — Range in amps (0.01, 0.1, 1, 3) or MIN\|MAX\|DEF `resolution` (numeric, optional)
`CONF:CURR:AC [{range}[,{resolution}]]`	command	Configure for AC current measurement
Details Parameters `range` (numeric, optional) `resolution` (numeric, optional)
`CONF:RES [{range}[,{resolution}]]`	command	Configure for 2-wire resistance measurement
Details Parameters `range` (numeric, optional) — Range in ohms (100 to 100e6) or MIN\|MAX\|DEF `resolution` (numeric, optional)
`CONF:FRES [{range}[,{resolution}]]`	command	Configure for 4-wire resistance measurement
Details Parameters `range` (numeric, optional) `resolution` (numeric, optional)
`CONF:FREQ [{range}[,{resolution}]]`	command	Configure for frequency measurement
Details Parameters `range` (numeric, optional) — Expected voltage amplitude for gate `resolution` (numeric, optional)
`CONF:PER [{range}[,{resolution}]]`	command	Configure for period measurement
Details Parameters `range` (numeric, optional) `resolution` (numeric, optional)
`CONF:CONT`	command	Configure for continuity test (threshold ~1000 ohm, beeper)
`CONF:DIOD`	command	Configure for diode test (1mA test current, reads voltage)
`CONF?`	query	Query current measurement configuration
Details Returns (string) Example: `"VOLT +1.00000000E+01,+1.00000000E-06"`

Measurement Execution

Trigger and read measurements

Command	Type	Description
`MEAS:VOLT:DC? [{range}[,{resolution}]]`	query	Configure, trigger, and return one DC voltage reading
Details Parameters `range` (numeric, optional) `resolution` (numeric, optional) Returns (numeric) — Voltage in volts Example: `+1.23456789E+00` Example `MEAS:VOLT:DC? 10,0.001`
`MEAS:VOLT:AC? [{range}[,{resolution}]]`	query	Configure, trigger, and return one AC voltage reading
Details Returns (numeric) Example: `+1.20000000E+02`
`MEAS:CURR:DC? [{range}[,{resolution}]]`	query	Configure, trigger, and return one DC current reading
Details Returns (numeric) Example: `+5.00000000E-02`
`MEAS:CURR:AC? [{range}[,{resolution}]]`	query	Configure, trigger, and return one AC current reading
Details Returns (numeric) Example: `+1.00000000E-01`
`MEAS:RES? [{range}[,{resolution}]]`	query	Configure, trigger, and return one 2-wire resistance reading
Details Returns (numeric) Example: `+1.00000000E+03`
`MEAS:FRES? [{range}[,{resolution}]]`	query	Configure, trigger, and return one 4-wire resistance reading
Details Returns (numeric) Example: `+1.00000000E+03`
`MEAS:FREQ? [{range}[,{resolution}]]`	query	Configure, trigger, and return one frequency reading
Details Returns (numeric) Example: `+1.00000000E+03`
`MEAS:PER? [{range}[,{resolution}]]`	query	Configure, trigger, and return one period reading
Details Returns (numeric) Example: `+1.00000000E-03`
`READ?`	query	Trigger and return one reading using current configuration
Details Returns (numeric) — Measurement result in current function's units Example: `+1.23456789E+00`
`INIT`	command	Initiate measurement and place in wait-for-trigger state
`FETCH?`	query	Return stored readings from internal memory (no new trigger)
Details Returns (numeric) — Comma-separated readings Example: `+1.23456789E+00,+1.23456790E+00`
`R? [{max_count}]`	query	Read and remove readings from memory; optionally limit count
Details Parameters `max_count` (numeric, optional) — Maximum readings to return Returns (numeric) Example: `+1.23456789E+00`

Trigger

Trigger system configuration

Command	Type	Description
`TRIG:SOUR {source}`	command	Set trigger source
Details Parameters `source` (enum) — BUS=*TRG/GET, IMM=immediate, EXT=rear panel Values: `BUS`, `IMM`, `EXT`
`TRIG:SOUR?`	query
Details Returns (string) Example: `IMM`
`TRIG:DEL {seconds}`	command	Set trigger delay
Details Parameters `seconds` (numeric) — Delay in seconds (0 to 3600) or MIN\|MAX\|DEF
`TRIG:DEL?`	query
Details Returns (numeric) Example: `+0.00000000E+00`
`TRIG:DEL:AUTO {state}`	command	Enable/disable automatic trigger delay
Details Parameters `state` (enum) Values: `ON`, `OFF`
`TRIG:COUN {count}`	command	Set number of triggers to accept before returning to idle
Details Parameters `count` (numeric) — 1 to 50000, or MIN\|MAX\|INF
`TRIG:COUN?`	query
Details Returns (numeric) Example: `+1`
`SAMP:COUN {count}`	command	Set number of readings per trigger
Details Parameters `count` (numeric) — 1 to 50000 or MIN\|MAX
`SAMP:COUN?`	query
Details Returns (numeric) Example: `+1`

Measurement Parameters

Detailed configuration of measurement parameters

Command	Type	Description
`VOLT:DC:RANG {range}`	command	Set DC voltage range manually
Details Parameters `range` (numeric) — 0.1, 1, 10, 100, 1000 or MIN\|MAX
`VOLT:DC:RANG?`	query
Details Returns (numeric) Example: `+1.00000000E+01`
`VOLT:DC:RANG:AUTO {state}`	command	Enable/disable DC voltage autoranging
Details Parameters `state` (enum) Values: `ON`, `OFF`
`VOLT:DC:NPLC {nplc}`	command	Set integration time in power line cycles
Details Parameters `nplc` (numeric) — 0.02, 0.2, 1, 10, 100 or MIN\|MAX Values: `0.02`, `0.2`, `1`, `10`, `100` Note: Higher NPLC = better resolution but slower. 100 NPLC = 6.5 digits.
`VOLT:DC:NPLC?`	query
Details Returns (numeric) Example: `+1.00000000E+01`
`VOLT:DC:RES {resolution}`	command	Set DC voltage resolution directly
Details Parameters `resolution` (numeric)
`INP:IMP:AUTO {state}`	command	Enable/disable high-impedance (>10G ohm) input on 100mV and 1V ranges
Details Parameters `state` (enum) Values: `ON`, `OFF` Note: When OFF, input impedance is 10M ohm on all ranges. When ON, >10G ohm on 100mV and 1V DC ranges.
`INP:IMP:AUTO?`	query
Details Returns (string) Example: `0`
`VOLT:AC:BAND {bandwidth}`	command	Set AC voltage bandwidth
Details Parameters `bandwidth` (numeric) — 3, 20, 200 Hz or MIN\|MAX Values: `3`, `20`, `200` Note: Lower bandwidth = more accurate for low frequencies but slower settling
`ZERO:AUTO {state}`	command	Enable/disable autozero for DC measurements
Details Parameters `state` (enum) Values: `ON`, `OFF`, `ONCE` Note: ONCE performs single zero then disables. OFF doubles measurement speed.

Math Operations

Built-in math and null offset functions

Command	Type	Description
`CALC:FUNC {function}`	command	Select math function
Details Parameters `function` (enum) — NULL=offset, DB=dB relative, DBM=dBm, AVER=statistics, LIM=limit test Values: `NULL`, `DB`, `DBM`, `AVER`, `LIM`
`CALC:STAT {state}`	command	Enable/disable selected math function
Details Parameters `state` (enum) Values: `ON`, `OFF`
`CALC:NULL:OFFS {value}`	command	Set null offset value
Details Parameters `value` (numeric) — Offset value in current measurement units
`CALC:NULL:OFFS?`	query
Details Returns (numeric) Example: `+0.00000000E+00`
`CALC:AVER:MIN?`	query	Query minimum reading since statistics cleared
Details Returns (numeric) Example: `+1.20000000E+00`
`CALC:AVER:MAX?`	query	Query maximum reading since statistics cleared
Details Returns (numeric) Example: `+1.30000000E+00`
`CALC:AVER:AVER?`	query	Query average of all readings since statistics cleared
Details Returns (numeric) Example: `+1.25000000E+00`
`CALC:AVER:COUN?`	query	Query number of readings taken since statistics cleared
Details Returns (numeric) Example: `+100`
`CALC:LIM:LOW {value}`	command	Set lower limit for limit test
Details Parameters `value` (numeric)
`CALC:LIM:UPP {value}`	command	Set upper limit for limit test
Details Parameters `value` (numeric)
`CALC:LIM:LOW?`	query
Details Returns (numeric) Example: `+0.00000000E+00`
`CALC:LIM:UPP?`	query
Details Returns (numeric) Example: `+0.00000000E+00`

System

System configuration and queries

Command	Type	Description
`SYST:ERR?`	query	Read and remove one error from error queue
Details Returns (string) — Error code and message Example: `+0,"No error"`
`SYST:VERS?`	query	Query SCPI version
Details Returns (string) Example: `1994.0`
`DISP {state}`	command	Turn front panel display on/off
Details Parameters `state` (enum) Values: `ON`, `OFF` Note: Turning display off improves measurement speed by ~10%
`DISP:TEXT "{message}"`	command	Display custom text on front panel (up to 12 chars)
Details Parameters `message` (string) — Up to 12 characters Example `DISP:TEXT "TESTING"`
`DISP:TEXT:CLE`	command	Clear custom display text and return to normal display
`SYST:BEEP`	command	Issue a single beep
`SYST:BEEP:STAT {state}`	command	Enable/disable beeper
Details Parameters `state` (enum) Values: `ON`, `OFF`
`DATA:POIN?`	query	Query number of readings stored in internal memory
Details Returns (numeric) Example: `0`

Output Format

Control the format of returned data

Command	Type	Description
`FORM:DATA {format}`	command	Set data transfer format
Details Parameters `format` (enum) — ASC=ASCII text, REAL=IEEE 754 binary Values: `ASC`, `REAL,32`, `REAL,64` Note: REAL formats are faster for bulk data transfer but require binary parsing
`FORM:DATA?`	query
Details Returns (string) Example: `ASC`

Common Workflows

Measure DC Voltage

Take a single DC voltage measurement on the 10V range with 6.5-digit resolution

Reset to known state

*RST

Clear status registers

*CLS

Configure for DC voltage, 10V range, max resolution

CONF:VOLT:DC 10,MIN

Set 100 NPLC for maximum resolution

VOLT:DC:NPLC 100

Enable high-impedance input

INP:IMP:AUTO ON

Trigger and read one measurement

READ?

Expected: +X.XXXXXXXXE+XX

Fast Multi-Reading Burst

Capture 100 DC voltage readings at maximum speed

Reset to known state

*RST

Configure DC voltage, autorange

CONF:VOLT:DC

Set fastest integration (4.5 digits)

VOLT:DC:NPLC 0.02

Disable autozero for speed

ZERO:AUTO OFF

Turn off display for speed

DISP OFF

Set trigger count to 100

TRIG:COUN 100

Set immediate trigger

TRIG:SOUR IMM

Initiate measurement sequence

INIT

Wait for completion

*OPC?

Expected: 1

Fetch all readings

FETCH?

Expected: Comma-separated values

Re-enable display

DISP ON

4-Wire Resistance with Null

Measure 4-wire resistance with lead-resistance null compensation

Reset to known state

*RST

Configure 4-wire resistance

CONF:FRES

Set high resolution

VOLT:DC:NPLC 10

Short test leads together, then null the reading

READ?

Record this value for the null offset

Enable null math function

CALC:FUNC NULL

Set null offset to the shorted reading

CALC:NULL:OFFS {shorted_reading}

Enable math

CALC:STAT ON

Connect DUT and measure

READ?

Expected: Resistance with lead compensation