Agilent LCR Meter Teardown

Since 1999, one of the more popular manufacturers of test equipment has been Agilent, the spun-off former instrument division of Hewlett-Packard. From simple multimeters to fully-equipped oscilloscopes, they have been covering every corner of this particular market. And, with the help of [Kerry Wong] and his teardown of an Agilent LCR meter, we can also see that they’ve been making consistent upgrades to their equipment as well.

The particular meter that [Kerry] took apart was an Agilent U1731B, a capable LCR (inductance, capacitance, resistance) meter. He had needed one for himself and noted that while they’re expensive when new, they can be found at a bargain used, but that means dealing with older versions of hardware. For example, his meter uses an 8-bit ADC while the more recent U1733 series uses a 24-bit ADC. The other quality of this meter that [Kerry] made special note of was how densely populated the circuit board is, presumably to save on the design of a VLSI circuit.

While we don’t claim to stump for Agilent in any way, it’s good to know that newer releases of their equipment actually have improved hardware and aren’t just rebadged or firmware-upgraded versions of old hardware with a bigger price tag attached. Also, there wasn’t really any goal that [Kerry] had in mind besides sheer curiosity and a willingness to dive deep into electronics details, as those familiar with his other projects know already.

Playing Doom on Keysight Oscilloscope via Windows CE

We all know the drill when buying a digital oscilloscope: buy the most hackable model. Some choose to void the warranty right away and access features for which the manufacturer has kindly provided all the hardware and software but has disabled through licensing. Few of us choose to tap into the underlying embedded OS, though, which seems a shame.

When [Jason Gin]’s scope started giving him hints about its true nature, he decided to find a way in. The result? An oscilloscope with a Windows desktop that plays Doom. The instrument is a Keysight DSOX1102G which [Jason] won during the company’s “Scope Month” giveaway. Relatively rare system crashes showed the familiar UI trappings of Windows CE.

Try as he might, [Jason] couldn’t get the scope to crash on cue — at least not until he tried leaving an external floppy drive plugged into the USB port on startup. But in order to use the desktop thus revealed, a keyboard and mouse were needed too. So he whipped up a custom USB switch cable, to rapidly toggle in the keyboard and mouse after the crash. This gave him the keys to the kingdom, but he still had a long way to go. We won’t spoil the story, but suffice it to say that it took [Jason] a year and a half, and he learned a lot along the way.

It was nice to hear that our review of the 1000X series scopes helped [Jason] accomplish this exploit. This hack’s great for bragging rights, as one way to prove you’ve owned a system is telling people it runs Doom!

Current Measurement with Oscilloscopes

What do a Rogowski coil, a magnetic core, and a hall effect sensor have in common? They are all ways you can make oscilloscope probes that measure current. If you think of a scope as a voltage measurement device, you ought to watch the recent video from Keysight Technology (see below). It is true that Keysight would love to sell you a probe, but the video is not a sales pitch, just general technical information about making current measurements with an oscilloscope.

Of course, you can always measure the voltage across a shunt resistor — either one that is naturally in the circuit or one you’ve put inline just for measuring purposes. But if you add a resistor it will change the circuit subtly and it may have to handle a lot of power.

The Keysight video points out that there are different probes for different current measurement regimes. High current, medium current, and low current all use different probes with different technologies. The video is only about 6 minutes long and if you’ve never thought about measuring current with a scope, it is worth watching.

The video shares some high-level details of how the current probes work — that’s where the Rogowski coil comes in, for example. Of course, you can’t expect a vendor to tell you how to build your own current probes. That’s OK, though, because we will. Current probes are often expensive, but you can sometimes pick up a deal on a used one.

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Nuts About Volts

Among multimeters one instrument stands far and above the rest. An object desired for its accuracy, resolution and shear engineering beauty. I speak of course of the HP 3458A. That’s right, not Keysight, not even Agilent (though of course it goes by those brands too). The 3458A was released in 1989, when HP was still… well… HP. An elegant meter from a more civilized age. As the HP Journal documents, the 3458A was a significant engineering feat and has remained in production (and largely unchallenged) for the last 26 years.

keyBut what, you might ask, makes the 3458A such a significant and desirable instrument? It’s all in the digits. The 3458A is one of the few 8.5 digit multimeters available. It is therefore sensitive to microvolt deflections on 10 volt measurements. It is this ability to distinguished tiny changes on large signals that sets high precision multimeters apart. Imagine weighing an elephant and being able to count the number of flies that land on its back by the change in weight. The 3458A accomplishes a similar feat.

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EEPROM hack unlocks crippled features in Agilent multimeter and LCR meter

u1241a-agilent-hack

[Gnif] was doing what any good hacker does… poking around the insides of one of his tools to see how it works. While in there, he discovered that an EEPROM hack could make the Agilent U1241A function like the U1242A.

If you’re into this kind of thing the Rigol 1052e hack should have already popped to mind. That was a firmware crippled device that, when unlocked, made the cheaper model behave the same ways as it’s $400 more expensive sibling. This doesn’t have quite the same impact, as the price difference is somewhere between $20-$100. Still, this stuff is just cool, right?

A few posts down in the thread linked above [Gnif] shares the story of how he found the hack. After shorting the i2c lines of the EEPROM while powering up the meter he was able to see that the device initializes a lot of its values to 0xFF when it can’t find the stored data. The next step was to use an STM32 board to dump the EEPROM contents. With the backup file stored safely he started changing values and reflashing the chip. Through this process he discovered that switching one byte from 0x01 to 0x02 enabled the higher model’s features. It also works for upgrading the U1732C to the U1733C feature set.