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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HP A front face.
Discussion is very welcome thru comment section or at our own IRC chat server: Table of contents Table Of Contents Rear Terminal Offset Test To be manal, contrast of this LCD got bit worse, but readings are still clearly visible. 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. It was common problem in other instrument HP Areading incorrect resistances when connections were loose.
This is good, even though not as impressive as HP A tweaking.
This stable 2V level supplied to voltage-current converter around Ua,Q with current setting by resistor R Preliminary Calibration Procedures This is non-traceable calibration for education purpose only. Special circuitry protects calibration data from unauthorized or random overwrite. Linear power regulator and optoisolation interface between the domains Outguard earth-referenced domain contains of: That makes possibility of rear back-light impossible.
Also calibration commands protected by password, which can be configured by user following special procedure.
It was the most troublesome, to pick and sort Q FET replacement. First rule of repair — do not change or fix things, that are still working fine.
HP 3457A Operating Instructions Manual
Also as bonus HP promoted ability to get 7th digit from special register access. Ac Voltage Function Gain Test HP A digital out-guard section Theory of operation, how things work Heart of the meter, Hp345a built using same principle as A, but now majority of critical components switches, comparator, current setting resistor networks, logics and clock tree is embedded in proprietary hybrid ASIC U Replacement Q matching One kind person my kind regards presented me with thin copper foil with adhesive layer.
Rear mxnual of the LCD have metal shield, which is obviously not transparent.
Likely, manuql contributors to noise performance are C Q U U Now we have just two more things to do. Suspects are listed below: Ac Convertor a3 Assembly Removal Reference voltage source is same module from A, using LM ovenized buried zener circuit. Final test data rainbow with all tested FET s: Even with shorted input, when reference noise irrelevant to ADC! Different non-modified HP A performance test, as received, 4-wire resistance function.
| Tweaks and mods for HP A digit DMM
To my opinion, this was bit overdue addition, as previous model, A even with official specifications without any tweaks can be more precise and less noisy than A. R trimpot adjutment for offset correction There is special procedure for voltage offset correction, but we will get back to it later.
Resistance hp345a7 for current measurement function.
Note, that on low voltage ranges 0. Replacement foil resistors S After Q replacement with faster curve than original and U more gain input amplifier circuitry started to oscillate with frequency majual kHz. When test jig controlled remotely by PC position of RP1 is in middle. This opamp provide most hp3457z the gain. On ranges 30 mV, mV and 3 V amplifier gain later A is There is possibility to save and recall multiple operation modes with all function settings, even after power cycle.
Closest to the base range is 3 V, which is not best case for sensitive measurements, such as 7V reference output. So I got idea to prevent running this procedure for intermediate testing.
Suspects are listed below:. HP A with shields installed.