HP 3457A

**Hewlett-Packard 3457A**
Status	supported
Source code	hp-3457a
Counts	30300000
IEC 61010-1	450V p-p max
Connectivity	GPIB
Measurements	voltage, current, resistance, frequency, period
Features	autorange, readings memory, four-wire resistance
Website	keysight.com

The Hewlett-Packard 3457A is a 7.5 digits (30300000 counts) bench digital multimeter with GPIB connectivity.

Hardware

Precision Subsurface Zener Voltage reference: Linear Technology LM399
Analog board microprocessor: Intel 8051
Digital board microprocessor: Motorola 6800

Plug-in cards

The HP 3457A supports one plug-in card in the rear, which replaces the rear terminals. Two cards are supported by the device.

Rear terminals

The rear terminals provide the same five-terminal measurement capability as the front panel terminals. The rear terminal block can be replaced by one of the following relay multiplexer cards.

44491A Armature Relay Multiplexer

This card supports 10 input channels. The last two channels are dedicated to current measurements while the other wight can be configured for either two-terminal measurements, or four-wire resistance measurements.

8 - voltage, 2-wire resistance channels
4 - four-wire resistance channels
2 - current channels

44492A Reed Relay Multiplexer

This card supports 10 channels, multiplexable to the voltage inputs. It supports voltage, two-wire resistance and frequency measurements.

sigrok quirks

Driver design goals and quirks

The driver is designed for accuracy and precision rather than throughput. As a result, it does not use the DMM's FIFO memory, but instead focuses on getting maximum precision from each measurement. When the integration time is set to 10 or 100 powerline cycles, the driver will automatically read the HIRES register, and add the result to the reading to get 7.5 digit measurements. This is handled transparently.

Only one measurement unit is supported, irrespective of the number of channels provided by expansion cards. This means that all channels will measure the same quantity. Changing measurement type between channels is not supported. Another side-effect is that if a given channel does not support the current measurement quantity, the DMM will produce a measurement with open terminals.

Only the front or rear terminals, or expansion card may be selected at any given time. This is because certain firmware revisions do not like switching back and forth too fast between terminals.

Switching between channels is achieved using the scan-advance feature, using the SLIST and SADV commands. This method seems to work best on all tested hardware and firmware revisions of the 3457A. Manual channel switching generates a "Trig too fast" error that is only correctable with an upgrade of the primary processor board.

Connecting and configuring the DMM

The HP3457A can only be accessed via GPIB. On linux, it will most likely be accessed with libgpib. The conn parameter will then be of the form "libgpib/<device_name>", where device_name is the name entry be specified in a gpib.conf device section.

The device supports a configurable ADC integration time based on the number of powerline cycles. This can be specified by using the nplc key. Since there is no way to query the measurement quantity, it should be specified before starting an acquisition, else the unit will not be reported. This is done via the measured_quantity key.

For example, to read two voltage samples from libgpib device hp3457a, with 10 powerline cycles integration time:

sigrok-cli --driver=hp-3457a:conn=libgpib/hp3457a \
  --samples 2 \
  --config "measured_quantity=voltage:nplc=10"

Photos

Hardware Revision 6

Device with the top cover removed. The analog section is hidden under two metal shields
Overview of the analog section
Analog section, riser board
Voltage reference board
Analog section, relays
Flyback diodes for the relays are nicely lined up
Mains input and transformer
Digital section, lithium NVRAM baterry