TONE 9: a beep when reading. Here is the whole stuff with my program running. While the HP is sleeping, we can use the display of the multimeter to keep track of essential informations for example the average to follow the treatment. We can use thermo resistors or photo resistors to the Ohmmeter to observe temperature or light. Program power consumption of a device: This program computes the power consumption of a device in KWH. Look at the picture: The cable from the power strip was rerouted to make the current go through the multimeter.
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Posted on February 23, by modemhead Hewlett-Packard has built a reputation for quality bench multimeters every bit as impressive as Fluke has for the handheld variety. Basic 1-year DCV accuracy is 0.
The A has ever so slightly better accuracy figures and adds a 30mV range. This unit arrives in a completely non-functional state. The remains of a Spanish-language calibration sticker on the back suggests it was maintained in a calibration program at some point in its lifetime. The entire analog section is shielded with a metal cover. The analog-to-digital converter is a custom HP part in a ceramic package. The character alpha-numeric LCD assembly has two COB-style drivers and is connected to the main board with a small ribbon cable.
The keypad board is mounted to the main board with a small bracket holding an elastomeric connector strip. The microprocessor has an HP part number, but looking in the service manual reveals that it is an , which is a RAM-only version of the A whopping bytes of RAM. Firmware is contained in external ROM. This particular unit is sourced from National Semiconductor and has a date code. The transformer-isolated HP-IL interface is in the back alongside the power supply circuitry. The power transformer has four taps to easily change the mains input to different international voltage levels.
Since the unit does not power up, first thing to check is the power supply. A small black mark on the element inside the glass mains fuse is a good clue that something has gone awry. A quick continuity check confirms that it is indeed blown.
Small problem. The fuse is rated mA and I do not have an exact replacement handy. Obviously some unknown fault has caused the original fuse to blow, so substituting a higher value and then smoke testing it would be a dumb idea.
This will tell me if the fault condition still exists, or whether it was some transient that caused the fuse to blow originally. Starting at 0V on the Variac and ramping up slowly, I get to about 35V and the current is already measuring mA.
The fault condition must still exist. Playing the Odds Instead of studying the schematic like a proper engineer, I just go with probabilities and start checking diodes in the power supply section at the back. Sure enough, there is a group of six diodes surrounding four capacitors, and five of them measure as a dead short. Now they test OK, out of circuit. I removed another pair and they test OK as well. Checking across the now-empty diode pads with an ohm-meter shows that the short or shorts still exist on the board somewhere.
Next item in the probability-of-failure category: capacitors. The four caps in the middle are the likely suspects, so I just remove them all. And 3 out of 4 of them measure as dead shorts. All three are 0. This is an unusual failure mode for electrolytic capacitors in my experience, but the ohm-meter does not lie.
All four capacitors get replaced. Another power-up attempt with the Variac shows only a 30 mA current draw for a full Vac input. The unit now powers up and passes the self-test, so hopefully there are no more faults. A quick check-out reveals that it is indeed functional on all ranges, and the calibration looks pretty good, except for AC current. See note 2 below the calibration check table. I would not use this meter for small-signal AC currents. In fact, experience has proved that AC or DC current measurements are not strong points for either the A or A.
One of them is 4-wire resistance measuring capability. Using separate source and sense test leads nullifies the test lead resistance, and allows for very accurate measurements below one ohm. The easiest way to perform a 4-wire measurement is by using Kelvin clips, as shown in the photo at right. I cheated to get the display to show a spot-on value. At this resolution, temperature effects on the resistance value are readily apparent.
It was reading a few counts high, I just put my fingers on the resistor for a few seconds to warm it up a bit.
2pcs HP Agilent 3468B Digital Multimeter
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HP 3468B PDF