This manual contains information relating to the installation, operation, performance testing, calibration, and service of the HP A Multimeter. The information. The HP A has seven functions with 3% to 6% digits of resolu- tion, extendable to 7% .. (). Opt Extra Operating and Service Manual. +$ Hp A Pdf User Manuals. View online or download Hp A Operating Instructions Manual, Service Manual.
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Outguard earth-referenced domain contains of: Replacement foil resistors S After Q replacement with faster curve than original and U more gain input amplifier circuitry started to oscillate with frequency around kHz.
Diodes CR, CR ensure operation of the current mirror with their voltage drop.
Resistors R and R act as load and define gain of the FET -amlifier, while current mirror circuit around Ua,Q balance equal DC current between the sides, increasing overall gain as result.
Areas where A have worse spec marked in red color. Sampling rate was equal to 0. R help to maintain balance when input is shorted, or in other words — cancel out voltage offset. Recommended Test Equipment Often modification result was negative performance got worseso reverse modification was required to determine what went wrong. Analog Devices ADA This information is displayed on the screen and operator is expected to adjust R for best result.
Higher voltage ranges are even trickier. HP A internal calibration RAM battery check Special circuitry protects calibration data from unauthorized or random overwrite.
So in next chapter we will try some experiments for first four circuits.
HP 3457A Manuals
Dc Current Function Offset Test Low ranges like 0. Linear power regulator manuql optoisolation interface between the domains Outguard earth-referenced domain contains of: Rear Lnput Performance Tests standard Manuall CR and CR protect opamp Ub from overload conditions. Mznual and modifications were tested on actual single HP A unit, and may or may not work in your particular instrument.
Make sure total height of the component in board is not taller then 12 mm, as there is AC module PCBA above the circuitry here. Dc Voltage Performance Tests Base range, which is 3. Rear Terminal Offset Test Disclaimer Redistribution and use of this article or any images or files referenced in it, in source and binary forms, manuzl or without modification, are permitted provided that the following conditions are met: Theory Of Operation Disconnect everything from the meter, including mains, GPIB and input cables.
Some might think that HP A is ancient technology instrument, and it should be very easy just to swap some opamps and components to modern high-performance devices, and everything will become much better. First I check if the adjustment necessary at all why to waste time on extra drift.
In service manual this procedure was explained for only case when self-test diagnistics related to this section unable to pass. HP A original Q matching.
| Tweaks and mods for HP A digit DMM
Hp a General Purpose Multiplexer Key importance at this np3457a to probe output with oscilloscope, to ensure stable operation without any oscillation, with actual DC signal applied on the input, from zero all the way to the full scale 3 V. More details presented below.
This module even have same HP part number. Many of inteface and overall design ideas in this meter are used as a base for later HP A monsters.
After Q replacement the complete input amplifier balance had to be adjusted and re-calibrated. Connection should not break if you just apply some force to the cable, big enough to lift the meter edge from the table. Overall block diagram Inguard isolated section has next circuits: Dc Current Offset Calibration On alternating voltage, A is much weaker than older A.
All this had to be reverted to original state in the end result, as noise only got worse. Dc Current Function HP A input frontend and signal manua schematics. Closest to the base hp3457s is 3 V, which is not best case for sensitive measurements, such as 7V reference output. Redistribution and use of this article or any images or files referenced in it, in source and binary forms, with or without manuxl, are permitted provided that the following conditions are met:.
This stable 2V level supplied to voltage-current converter around Ua,Q with current setting by resistor R Cost of maintenance hp3457q these meters is reachable even for hobby users to use a lab working tool.
A Digital Multimeter [Obsolete] | Keysight (formerly Agilent’s Electronic Measurement)
Perhaps because of this note in service manual typical calibration in the service shops does not include this calibration either. Turn the meter upside down, undo 6 screws if there are original rubber gaskets, there is no need to remove screws from cover.
Also as bonus HP promoted ability to get 7th digit from special register access. Basic DCV accuracy is specified better than 5 ppm. Preliminary Calibration Procedures R trimpot adjutment for offset correction.
Dc Volts Gain Calibration Everything else, like charge rate switches, counters and control logic integrated on U hybrid ASICor perform auxilary roles reset comparator Ua, switches. One kind person my kind regards presented me with thin copper foil with adhesive layer.