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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Basic DCV accuracy is specified better than 5 ppm. HP A can also use optional expansion card with multiplexer scanner, to add up to 10 channels for input signals. Many of inteface and overall design ideas in this meter are used as a base for later HP A monsters. Redistribution and use of this article or any images or files referenced in it, in source and binary forms, with or without modification, are permitted provided that the following conditions are met:.
All information posted here is hosted just for education purposes and provided AS IS. In no event shall the author, xDevs. Details and modifications were tested on actual single HP A unit, and may or may hp3457x work in your particular instrument.
HP Journal archive, issue February. Analog Devices ADA This meter was also first in HP system-level flagship line to feature integrated measurements for both direct and alternating current and alternating voltage frequency and period. HP A bottom side. This means that disassembly and cover removals not required for adjustment and calibration with few exceptions, covered later.
Hp345a7 coefficients are stored in SRAMwhich is powered even if instruments powered off, with help of on-board lithium battery.
Yes, it also does mean that calibration will be lost if meter too old and battery discharged. Special circuitry protects calibration data from unauthorized or random overwrite.
Also calibration commands protected by password, which can be configured by user following special procedure.
There is possibility to save and recall multiple operation modes with all function settings, even after power cycle. Also each function and mode can be configured either from front panel or remotely over GPIB interface. HP A front face. Also as bonus HP promoted ability to get 7th digit from special register access.
To my opinion, this was bit overdue addition, as gp3457a model, A even with official specifications without any tweaks can be more precise and less noisy than A. Sounds too good to be true? Check the table below with uncertainty calculations. Data from specs for 24 hour and 90 day period was used.
Low ranges like 0. Areas where A have worse spec marked in red color. On alternating voltage, A is much weaker than older A. Note that A conversion from ADC is actually 7 digits, but least digit is averaged out and not reported to the front-end, nor the GPIB mankal remote controller. Important feature, absent from previous A, is ability to select front or rear terminal input by remote GPIB command.
As result there is no mechanical switch on front panel to change terminal side manually. Also manal unit has least weight in class, due to use of hp3547a instead of metal as covers material. Inguard shield removed, revealed AC and front end main board. More details presented manjal. Inguard isolated section has next circuits: Electronic input terminal switching. COTO relay for front end. Resistance shunts for current measurement function.
Input amplifier after my modifications. Linear power regulator and optoisolation interface between the domains.
Outguard earth-referenced domain contains of: HP A digital out-guard section. Heart of the meter, ADC built using same principle as A, but now majority of critical components switches, comparator, current setting resistor maual, logics and clock tree is embedded in proprietary hybrid ASIC U HP A U hybrid.
Reference voltage source is same module from A, using LM ovenized buried zener circuit. This module even have same HP part number. There is no service manual schematics for this module in A documents, but such schematics available in A.
Hmm, hold hp3457x a moment?
3457A Digital Multimeter
mnaual How did that happened? This is not a mistake, but a design approach of the A. To scale input signal amplitude input amplifier is always engaged, but has different gain coefficient.
On ranges 30 mV, mV and 3 V amplifier gain later A is Higher voltage ranges are even trickier. For 30 V and V additional U hybrid design block diagram. As result of such complex arrangement A front-end does have more input noise compared mannual A, and also does not have 1: Closest to the base range is 3 V, which is not best case for hp345a measurements, such as 7V reference output. Modifications for A input amplifier.
Manuzl stable 2V level supplied to voltage-current converter around Ua,Q with current setting by resistor R R help to maintain balance when input is shorted, or in other words — cancel out voltage offset. R trimpot adjutment for offset correction. 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.
Actual amplifier part is Q, and Q help for constant voltage between source and drain of Q Diodes CR, CR ensure operation of the current mirror with their voltage drop.
CR and CR protect opamp Ub from overload conditions. This opamp provide most of the gain. Worth to note, that this operational amplifier must be stable with both high and low gains, and as we will see later, most troublesome range for stability is 3 V. So main interest go to other possible noise sources. Suspects are listed below:. Here is composite integrator Q,U with integrating capacitor C and pre-amp for comparator circuit U,R,R Everything else, like charge rate switches, counters and control logic integrated on U hybrid ASICor perform auxilary roles reset comparator Ua, switches.
These auxiliary circuits do not affect noise performance of the ADC. Likely, largest contributors to noise performance are C Q U U Some might think that HP A is ancient technology instrument, and it should be very easy just mahual swap some opamps and components to modern hp457a devices, and everything will become much better.
Well, in analog design world things manal much more complicated, and up3457a components without understanding what mmanual circuit do is a road to a disaster and broken equipment. Upgrades and modifications on this HP A were attempted for long time, multiple times for period over a year. The longest process was getting required component samples.
Another time consuming challenge — complex approach type.
File:HP A operating – Hive13 Wiki
That mean each modification test is full reassembly, few hours warmup and then multiple hours for datalogging each low range separately! I tried to combine modifications in groups, so can test multiple things at same time, when that was possible. Often modification result was negative performance got worseso reverse modification was required to determine what went wrong. Hope this can be helpful for other HP A owners. Additional temperature sensor and output BNC port for it.
Adding common mode ferrite choke and removing connections between reference module and mainboard does not need additional explaining either. Since all microchips in HP A are in thru-hole type DIP style, all replaced components are carefully desoldered and positions on the board populated with high-quality collet-type sockets.
This allows to experiment easy without risk of damaging manal board taking everything apart for each component swap. LT circuitry near DCV reference. All this had to be reverted to original state in the end result, as noise only got worse.
Replaced opamps with collet sockets. I did not want to wait, so adapter board bodge to the rescue to fit two chips in DIP 8 bp3457a. HP A original damaged R resistor.
Replacement foil resistors S After Q replacement with faster curve than original and ,anual more gain input amplifier circuitry started to oscillate with frequency around kHz. Capacitors used for stability compensation. I used middle sweet spot device for replacement Q Key importance at this stage 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.
If there is lack of compensation, then amplifier will work normally when input voltage is zero or less then 0. It was the most troublesome, to pick and sort Q FET replacement. DIY voltage-current curve plot detector. This was required to enable trimpot RP1 setting for both negative and positive gate voltage.