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GPIB Catalog

Hewlett-Packard 53131A

Hewlett-Packard

53131A

225 MHz universal frequency counter/timer

frequency_counter SCPI
Hewlett-Packard 53131A universal frequency counter at Owens Valley Radio Observatory
cgk, CC BY 2.0, via Wikimedia Commons
Default Address 3
Termination LF
IEEE 488.2 Yes
IDN Patterns
HEWLETT-PACKARD,53131A,*,*AGILENT TECHNOLOGIES,53131A,*,*
Documentation

The 53131A is a 225 MHz universal counter produced by HP (later Agilent/Keysight) from the mid-1990s. It features two 225 MHz channels with an optional third channel extending to 12.4 GHz. The reciprocal counting technique provides high resolution at all frequencies -- not just at high frequencies like traditional counters. Resolution is determined by gate time, not input frequency. Standard timebase is a 10 MHz TCXO; optional high-stability OCXO or rear-panel external 10 MHz reference input available. The 53132A is the higher-resolution sibling (12-digit/s vs 10-digit/s). Very common in calibration labs and production test. GPIB is standard on all units.

Status Byte

Section titled “Status Byte”
Bit 7Bit 6Bit 5Bit 4Bit 3Bit 2Bit 1Bit 0
Operation CompleteRQS/MSSESBMAVQuestionable DataError QueueUnusedUnused
Operation summary bitRequesting service / Master summary statusEvent status byte summary bitMessage available in output bufferQuestionable data summary bitOne or more errors in error queueNot usedNot used

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

Commands

Section titled “Commands”

IEEE 488.2 Common Commands

Section titled “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,53131A,0,4806
*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, non-zero for fail
Details
Returns (numeric)
Example: 0
Note: Takes several seconds to complete
*TRG command Trigger measurement from bus (requires trigger source BUS)
*WAI command Wait for all pending operations to complete before executing next command
*SAV {register} command Save current instrument state to non-volatile register
Details
Parameters
  • register (numeric) — Register number 0-9
*RCL {register} command Recall instrument state from non-volatile register
Details
Parameters
  • register (numeric) — Register number 0-9

Measurement Configuration

Section titled “Measurement Configuration”

Configure measurement function and parameters. CONF sets up the measurement without triggering; MEAS configures, triggers, and returns a reading in one operation.

Command Type Description
CONF:FREQ [{expected}[,{resolution}[,{channel}]]] command Configure for frequency measurement on specified channel
Details
Parameters
  • expected (numeric, optional) — Expected frequency in Hz or MIN|MAX|DEF Default: DEF
  • resolution (numeric, optional) — Resolution in Hz or MIN|MAX|DEF Default: DEF
  • channel (numeric, optional) — Input channel (@1 or @2) Default: 1
Example CONF:FREQ 1E6,1,(@1)
CONF:FREQ? query Query current frequency configuration
Details
Returns (string)
Example: "FREQ +1.00000000E+06,+1.00000000E+00"
CONF:PER [{expected}[,{resolution}[,{channel}]]] command Configure for period measurement on specified channel
Details
Parameters
  • expected (numeric, optional) — Expected period in seconds or MIN|MAX|DEF
  • resolution (numeric, optional) — Resolution in seconds or MIN|MAX|DEF
  • channel (numeric, optional) — Input channel (@1 or @2) Default: 1
Example CONF:PER DEF,DEF,(@1)
CONF:PHAS [{expected}[,{resolution}]] command Configure for phase measurement between channel 1 and channel 2
Details
Parameters
  • expected (numeric, optional) — Expected phase in degrees or MIN|MAX|DEF
  • resolution (numeric, optional) — Resolution in degrees or MIN|MAX|DEF
Note: Phase is always measured from channel 1 to channel 2
CONF:TINT [{expected}[,{resolution}]] command Configure for time interval measurement (channel 1 start, channel 2 stop)
Details
Parameters
  • expected (numeric, optional) — Expected time interval in seconds or MIN|MAX|DEF
  • resolution (numeric, optional) — Resolution in seconds or MIN|MAX|DEF
Note: Start event on channel 1, stop event on channel 2
CONF:TOT [{channel}] command Configure for totalize (event counting) measurement
Details
Parameters
  • channel (numeric, optional) — Input channel (@1 or @2) Default: 1
Note: Counts threshold crossings. Gate control determines counting window.
CONF:FREQ:RAT [{expected}[,{resolution}[,{ch_num},{ch_den}]]] command Configure for frequency ratio measurement (numerator channel / denominator channel)
Details
Parameters
  • expected (numeric, optional) — Expected ratio or MIN|MAX|DEF
  • resolution (numeric, optional) — Resolution or MIN|MAX|DEF
  • ch_num (numeric, optional) — Numerator channel (@1 or @2) Default: 1
  • ch_den (numeric, optional) — Denominator channel (@1 or @2) Default: 2
Example CONF:FREQ:RAT DEF,DEF,(@1),(@2)
CONF? query Query current measurement configuration
Details
Returns (string)
Example: "FREQ +1.00000000E+06,+1.00000000E+00"
MEAS:FREQ? [{expected}[,{resolution}[,{channel}]]] query Configure, trigger, and return one frequency reading
Details
Parameters
  • expected (numeric, optional)
  • resolution (numeric, optional)
  • channel (numeric, optional) Default: 1
Returns (numeric) — Frequency in Hz
Example: +1.00000123E+06
Example MEAS:FREQ? 1E6,1,(@1)
MEAS:PER? [{expected}[,{resolution}[,{channel}]]] query Configure, trigger, and return one period reading
Details
Returns (numeric) — Period in seconds
Example: +9.99999877E-07
MEAS:PHAS? [{expected}[,{resolution}]] query Configure, trigger, and return one phase reading (ch1 to ch2)
Details
Returns (numeric) — Phase in degrees
Example: +4.50000000E+01
MEAS:TINT? [{expected}[,{resolution}]] query Configure, trigger, and return one time interval reading
Details
Returns (numeric) — Time interval in seconds
Example: +1.00000000E-06
MEAS:TOT? [{channel}] query Configure, trigger, and return a totalize count
Details
Returns (numeric) — Total event count
Example: +1.00000000E+05
MEAS:FREQ:RAT? [{expected}[,{resolution}[,{ch_num},{ch_den}]]] query Configure, trigger, and return one frequency ratio reading
Details
Returns (numeric) — Frequency ratio (dimensionless)
Example: +2.00000000E+00

Input Configuration

Section titled “Input Configuration”

Configure input channel coupling, impedance, attenuation, triggering level, slope, and filtering. Channel is specified as 1 or 2 (e.g., INP1: or INP2:). INP: with no suffix defaults to channel 1.

Command Type Description
INP{n}:COUP {coupling} command Set input coupling for specified channel
Details
Parameters
  • n (numeric) — Channel number (1 or 2) Values: 1, 2
  • coupling (enum) — AC coupling blocks DC offset; DC passes full signal Values: AC, DC
Example INP1:COUP DC
INP{n}:COUP? query Query input coupling for specified channel
Details
Returns (string)
Example: AC
INP{n}:IMP {impedance} command Set input impedance for specified channel
Details
Parameters
  • n (numeric) — Channel number (1 or 2)
  • impedance (enum) — 50 ohm (terminating) or 1 megohm (high-Z) Values: 50, 1E6
Example INP1:IMP 50
Note: 50 ohm provides proper termination for transmission lines; 1 megohm for high-impedance probing
INP{n}:IMP? query Query input impedance for specified channel
Details
Returns (numeric)
Example: +1.00000000E+06
INP{n}:ATT {attenuation} command Set input attenuation for specified channel
Details
Parameters
  • n (numeric) — Channel number (1 or 2)
  • attenuation (enum) — 1x (no attenuation) or 10x (20 dB attenuation) Values: 1, 10
Example INP1:ATT 1
INP{n}:ATT? query Query input attenuation for specified channel
Details
Returns (numeric)
Example: +1
INP{n}:FILT {state} command Enable/disable 100 kHz low-pass input filter for specified channel
Details
Parameters
  • n (numeric) — Channel number (1 or 2)
  • state (enum) Values: ON, OFF
Note: Filter removes high-frequency noise that could cause false triggers on low-frequency signals
INP{n}:FILT? query Query input filter state for specified channel
Details
Returns (string)
Example: 0
INP{n}:LEV {level} command Set trigger level (threshold) for specified channel
Details
Parameters
  • n (numeric) — Channel number (1 or 2)
  • level (numeric) — Trigger level in volts or MIN|MAX|DEF
Example INP1:LEV 0.5
Note: Range depends on coupling and attenuation settings. Typically -5.125V to +5.125V (1x, 50 ohm)
INP{n}:LEV? query Query trigger level for specified channel
Details
Returns (numeric) — Trigger level in volts
Example: +0.00000000E+00
INP{n}:LEV:AUTO {state} command Enable/disable automatic trigger level for specified channel
Details
Parameters
  • n (numeric) — Channel number (1 or 2)
  • state (enum) Values: ON, OFF
Note: When ON, counter automatically sets trigger level to ~50% of signal amplitude
INP{n}:LEV:AUTO? query Query automatic trigger level state for specified channel
Details
Returns (string)
Example: 1
INP{n}:SLOP {slope} command Set trigger slope (edge) for specified channel
Details
Parameters
  • n (numeric) — Channel number (1 or 2)
  • slope (enum) — POS = rising edge, NEG = falling edge Values: POS, NEG
Example INP1:SLOP POS
INP{n}:SLOP? query Query trigger slope for specified channel
Details
Returns (string)
Example: POS

Trigger and Measurement Execution

Section titled “Trigger and Measurement Execution”

Control the trigger system, sample count, and read measurement results

Command Type Description
TRIG:SOUR {source} command Set trigger source
Details
Parameters
  • source (enum) — BUS=*TRG/GET, IMM=immediate, EXT=rear panel external trigger Values: BUS, IMM, EXT
TRIG:SOUR? query
Details
Returns (string)
Example: IMM
TRIG:COUN {count} command Set number of trigger events to accept before returning to idle
Details
Parameters
  • count (numeric) — 1 to 1000000, or MIN|MAX|INF
TRIG:COUN? query
Details
Returns (numeric)
Example: +1
SAMP:COUN {count} command Set number of measurements per trigger event
Details
Parameters
  • count (numeric) — 1 to 1000000 or MIN|MAX
SAMP:COUN? query
Details
Returns (numeric)
Example: +1
INIT command Initiate measurement and place in wait-for-trigger state
READ? query Trigger and return one reading using current configuration (equivalent to INIT + FETCH?)
Details
Returns (numeric) — Measurement result in current function's units
Example: +1.00000123E+06
FETCH? query Return the last measurement result without triggering a new measurement
Details
Returns (numeric) — Last measurement result
Example: +1.00000123E+06
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: +1.00000123E+06
ABORT command Abort measurement in progress and return to idle trigger state

Gate Control

Section titled “Gate Control”

Configure the gate (arming) mechanism that determines how long the counter counts events. The gate directly controls measurement resolution for frequency and period measurements.

Command Type Description
FREQ:ARM:STAR:SOUR {source} command Set start arm source for frequency/period measurements
Details
Parameters
  • source (enum) — IMM=start immediately, EXT=wait for external start signal Values: IMM, EXT
Note: Most measurements use IMMediate start arm
FREQ:ARM:STAR:SOUR? query
Details
Returns (string)
Example: IMM
FREQ:ARM:STOP:SOUR {source} command Set stop arm (gate) source for frequency/period measurements
Details
Parameters
  • source (enum) — IMM=single event, EXT=external gate, TIM=timed gate, DIG=N digits of resolution Values: IMM, EXT, TIM, DIG
FREQ:ARM:STOP:SOUR? query
Details
Returns (string)
Example: TIM
FREQ:ARM:STOP:TIM {seconds} command Set gate time when stop arm source is TIMer
Details
Parameters
  • seconds (numeric) — Gate time in seconds (0.001 to 1000) or MIN|MAX|DEF
Example FREQ:ARM:STOP:TIM 1
Note: Longer gate time = higher resolution. 1s gate gives ~10 digits for 10 MHz signal. Default after *RST is 0.1s.
FREQ:ARM:STOP:TIM? query Query current gate time
Details
Returns (numeric) — Gate time in seconds
Example: +1.00000000E-01
FREQ:ARM:STOP:DIG {digits} command Set number of digits of resolution when stop arm source is DIGits
Details
Parameters
  • digits (numeric) — Number of resolved digits (3 to 15) or MIN|MAX
Example FREQ:ARM:STOP:DIG 10
Note: Counter automatically adjusts gate time to achieve requested number of digits
FREQ:ARM:STOP:DIG? query Query number of digits for auto-gate
Details
Returns (numeric)
Example: +10
TOT:ARM:STAR:SOUR {source} command Set start arm source for totalize measurements
Details
Parameters
  • source (enum) — IMM=start immediately, EXT=wait for external signal Values: IMM, EXT
TOT:ARM:STOP:SOUR {source} command Set stop arm source for totalize measurements
Details
Parameters
  • source (enum) — IMM=count forever until ABORT, EXT=external gate, TIM=timed gate Values: IMM, EXT, TIM
TOT:ARM:STOP:TIM {seconds} command Set totalize gate time when stop source is TIMer
Details
Parameters
  • seconds (numeric) — Gate time in seconds

Math and Statistics

Section titled “Math and Statistics”

Built-in statistical analysis and limit testing. Statistics accumulate over successive measurements until cleared.

Command Type Description
CALC:AVER:STAT {state} command Enable/disable statistical accumulation (min, max, mean, std deviation)
Details
Parameters
  • state (enum) Values: ON, OFF
Note: When enabled, each measurement is added to the statistics register. Use *RST or CALC:AVER:STAT OFF then ON to clear.
CALC:AVER:STAT? query Query whether statistics accumulation is enabled
Details
Returns (string)
Example: 0
CALC:AVER:COUN? query Query number of readings accumulated in statistics register
Details
Returns (numeric)
Example: +100
CALC:AVER:MIN? query Query minimum reading since statistics were last cleared
Details
Returns (numeric) — Minimum value in measurement units
Example: +9.99999900E+05
CALC:AVER:MAX? query Query maximum reading since statistics were last cleared
Details
Returns (numeric) — Maximum value in measurement units
Example: +1.00000010E+06
CALC:AVER:AVER? query Query arithmetic mean of all accumulated readings
Details
Returns (numeric) — Mean value in measurement units
Example: +1.00000001E+06
CALC:AVER:SDEV? query Query standard deviation of all accumulated readings
Details
Returns (numeric) — Standard deviation in measurement units
Example: +2.50000000E-01
CALC:MATH:STAT {state} command Enable/disable math operations (scale and offset)
Details
Parameters
  • state (enum) Values: ON, OFF
CALC:MATH:GAIN {value} command Set math scale factor (result = reading * gain + offset)
Details
Parameters
  • value (numeric) — Scale factor
CALC:MATH:GAIN? query
Details
Returns (numeric)
Example: +1.00000000E+00
CALC:MATH:OFFS {value} command Set math offset value (result = reading * gain + offset)
Details
Parameters
  • value (numeric) — Offset value in measurement units
CALC:MATH:OFFS? query
Details
Returns (numeric)
Example: +0.00000000E+00
CALC:LIM:STAT {state} command Enable/disable limit testing
Details
Parameters
  • state (enum) Values: ON, OFF
CALC:LIM:LOW {value} command Set lower limit for limit test
Details
Parameters
  • value (numeric) — Lower limit in measurement units
CALC:LIM:LOW? query
Details
Returns (numeric)
Example: +0.00000000E+00
CALC:LIM:UPP {value} command Set upper limit for limit test
Details
Parameters
  • value (numeric) — Upper limit in measurement units
CALC:LIM:UPP? query
Details
Returns (numeric)
Example: +0.00000000E+00
CALC:LIM:FAIL? query Query whether last measurement was within limits
Details
Returns (numeric) — 0=pass (within limits), 1=fail (outside limits)
Example: 0

System

Section titled “System”

System configuration, error handling, display, and beeper control

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 supported by instrument
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 slightly improves measurement throughput
DISP:TEXT "{message}" command Display custom text on front panel
Details
Parameters
  • message (string) — Text string to display (up to 16 characters)
Example DISP:TEXT "CALIBRATING"
DISP:TEXT:CLE command Clear custom display text and return to normal measurement display
SYST:BEEP command Issue a single beep from the front panel speaker
SYST:BEEP:STAT {state} command Enable/disable the beeper
Details
Parameters
  • state (enum) Values: ON, OFF
DATA:POIN? query Query number of readings stored in internal memory
Details
Returns (numeric)
Example: 0
SYST:TOUT {state} command Enable/disable measurement timeout
Details
Parameters
  • state (enum) Values: ON, OFF
Note: When ON, measurement will timeout if no valid trigger event occurs within the timeout period
SYST:TOUT:TIM {seconds} command Set measurement timeout period
Details
Parameters
  • seconds (numeric) — Timeout in seconds (1 to 1000)

Format

Section titled “Format”

Control the format of returned measurement data

Command Type Description
FORM:DATA {format} command Set data transfer format
Details
Parameters
  • format (enum) — ASC=ASCII text, REAL=IEEE 754 binary (32-bit or 64-bit) 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

Section titled “Common Workflows”

Measure Frequency

Section titled “Measure Frequency”

Measure frequency of a signal on channel 1 with a 1-second gate time for high resolution

1

Reset to known state

*RST
2

Clear status registers

*CLS
3

Configure for frequency measurement on channel 1

CONF:FREQ DEF,DEF,(@1)
4

Set gate time to 1 second for ~10-digit resolution

FREQ:ARM:STOP:SOUR TIM
5

Set the gate time value

FREQ:ARM:STOP:TIM 1
6

Enable auto trigger level

INP1:LEV:AUTO ON
7

Trigger and read the frequency

READ?
Expected: +X.XXXXXXXXE+XX (frequency in Hz)

Statistical Analysis

Section titled “Statistical Analysis”

Take 100 frequency readings and compute statistics (min, max, mean, standard deviation)

1

Reset to known state

*RST
2

Clear status registers

*CLS
3

Configure for frequency measurement

CONF:FREQ DEF,DEF,(@1)
4

Set 0.1s gate time

FREQ:ARM:STOP:SOUR TIM
5

Set gate time value

FREQ:ARM:STOP:TIM 0.1
6

Enable auto trigger level

INP1:LEV:AUTO ON
7

Enable statistics

CALC:AVER:STAT ON
8

Set sample count to 100

SAMP:COUN 100
9

Set trigger source to immediate

TRIG:SOUR IMM
10

Initiate measurement sequence

INIT
11

Wait for all measurements to complete

*OPC?
Expected: 1
12

Read number of accumulated readings

CALC:AVER:COUN?
Expected: +100
13

Read minimum frequency

CALC:AVER:MIN?
Expected: +X.XXXXXXXXE+XX
14

Read maximum frequency

CALC:AVER:MAX?
Expected: +X.XXXXXXXXE+XX
15

Read mean frequency

CALC:AVER:AVER?
Expected: +X.XXXXXXXXE+XX
16

Read standard deviation

CALC:AVER:SDEV?
Expected: +X.XXXXXXXXE+XX

Measure Time Interval

Section titled “Measure Time Interval”

Measure time interval between a rising edge on channel 1 and a rising edge on channel 2

1

Reset to known state

*RST
2

Configure for time interval measurement

CONF:TINT
3

Set channel 1 to trigger on rising edge

INP1:SLOP POS
4

Set channel 2 to trigger on rising edge

INP2:SLOP POS
5

Enable auto trigger level on channel 1

INP1:LEV:AUTO ON
6

Enable auto trigger level on channel 2

INP2:LEV:AUTO ON
7

Trigger and read the time interval

READ?
Expected: +X.XXXXXXXXE+XX (time in seconds)

High-Resolution Frequency with Digit Gate

Section titled “High-Resolution Frequency with Digit Gate”

Measure frequency using automatic gate sizing to achieve a specific number of digits of resolution

1

Reset to known state

*RST
2

Configure for frequency measurement

CONF:FREQ DEF,DEF,(@1)
3

Set stop arm source to digits mode

FREQ:ARM:STOP:SOUR DIG
4

Request 12 digits of resolution

FREQ:ARM:STOP:DIG 12
5

Enable auto trigger level

INP1:LEV:AUTO ON
6

Trigger and read

READ?
Expected: +X.XXXXXXXXXXE+XX (12-digit result)
7

Query actual gate time used

FREQ:ARM:STOP:TIM?
Expected: Gate time automatically selected

Totalize Events

Section titled “Totalize Events”

Count events on channel 1 over a 10-second gate window

1

Reset to known state

*RST
2

Configure for totalize on channel 1

CONF:TOT (@1)
3

Set start arm to immediate

TOT:ARM:STAR:SOUR IMM
4

Set stop arm to timed gate

TOT:ARM:STOP:SOUR TIM
5

Set gate time to 10 seconds

TOT:ARM:STOP:TIM 10
6

Set channel 1 coupling to DC

INP1:COUP DC
7

Set trigger level to 0.5V

INP1:LEV 0.5
8

Set trigger slope to rising edge

INP1:SLOP POS
9

Trigger and read total count

READ?
Expected: +X.XXXXXXXXE+XX (total event count)