A few months ago, we conducted an email interview with the Keysight Digital Multimeter team. This group has produced many classic products since the HP days, including the 3458A, 34401A, and 34970A. One question kept coming to mind: Why was the 34401A so successful, and what could they do after such a monumental achievement?
The interview was with Wayne H. Willis, the product manager for the multimeter team. Wayne joined Hewlett-Packard in 1979 and was the first to manage the production line. In his 1992 HP Journal, he wrote an article about using the VXI platform on automated test lines. He's known as a computer enthusiast.
During the interview, we also secretly took apart their new 34461A digital multimeter. The teardown details are in the second half of the article, along with the Q&A section.
We also got a photo of Wayne Willis from the HP Journal.
The interview was fascinating. In preparation, we took apart one of their 34461A units.
In the following article:
EEN refers to EENuts and WW refers to Wayne Willis.
EEN: Please tell us about your work on the Keysight multimeter team. Can you show us a team photo?
WW: Hello, everyone. I'm Wayne Willis, the R&D Manager for the 34461A and an Electronic Engineer. I joined HP in 1979 (38 years ago!). Every day, I work with R&D engineers and product marketing engineers to design and develop new products. Since the focus is on our digital multimeter, here's a photo of the design team. Our team includes young engineers and senior engineers with over 40 years of experience. Some even worked on the 34401A project. You can easily spot them—they have less hair...
This is the 3446X multimeter R&D team, and the engineers with less hair worked on the 34401A project.
EEN: Since the 34401A is the most successful product in HP-Agilent-Keysight history, did you celebrate when it was officially discontinued?
WW: Absolutely! We had a big celebration and held a grand "retirement" ceremony for the 34401A on December 1, 2016, the day it was discontinued. We gathered everyone who worked on the 34401A project, including R&D, marketing, and order management. Many have retired, making it a reunion of old friends. The event was hosted by the person responsible for the 34401A market. He shared many funny stories, reliving those times with everyone. It was touching and brought back a lot of memories.
EEN: As a participant, from your perspective, what factors made the 34401A so successful? Can you list the three most important reasons?
WW: The 34401A was truly a groundbreaking product. For $5.5k, it offered 6.5-digit accuracy and resolution, and its durability and reliability remain unmatched in the industry. Its success is the result of balancing low price, high performance, and ruggedness—exactly what users need.
EEN: What "superpowers" did you use to make the 34401A so successful and enduring? If you wanted to design a similarly successful product, what would be the biggest challenge?
WW: I think it might be due to the fact that the 34401A was HP's first product to undergo extensive market research before development. All market research results were aggregated into an analysis tool called House of Quality (HOQ), which was the first product development decision system proposed by Japanese companies in the 1980s. We detailed and prioritized customer feedback. The "quality house" system was innovative at the time and proved to be very effective, especially when trade-offs were needed. The first thing we considered was putting the user's needs first.
For instance, we all know that users want products to be strong and reliable. On one hand, we had to find ways to improve product quality and meet their demands. On the other hand, we also had to make them feel intuitive and reliable. That's why, in the final design of the 34401A, we added a rubber protective cover (bumper), which wasn't available in previous HP products. To this day, all our desktop instruments continue to feature this rubber sleeve, even influencing other manufacturers because it strongly meets customer expectations. (I feel teased...)
The most challenging part of designing a successful product is balancing cost, performance, and reliability. To meet these three requirements without compromise, you need to focus on the product's details and require a lot of innovation, collaboration, and mutual support between the R&D team, the order management team, and key suppliers. I'm glad we've done well.
EEN: As a member of the 34401A project, do you have any regrets?
WW: No, not at all. It's perfect. (Proud face...)
EEN: We’ve seen that the Multi-slope ADC has evolved to the fourth generation on the 34461A. What improvements have been made to this generation of technology? The new ADC system still uses a combination of multiple chips, but it’s possible to make a single chip in the future to achieve this.
WW: We continue to improve A/D algorithms and techniques in our multimeters. The earliest multi-slope integration technique evolved into the second generation (3458A and 34401A) and the third generation (34410/11A). In new products, we use the delta-sigma algorithm in the ADC design, which also improves the linearity of the test results. Precision ADC design requires the use of many devices, including reference levels, high-stability devices, matching resistor networks, high-impedance and matching low-leakage switching devices, A/D control circuits, etc. High-level chip integration has been ongoing, but we found that a single chip design couldn’t meet all the accuracy requirements we needed. Therefore, the current design is still based on multiple chips and devices. I believe that technology will continue to evolve, and it may not be long before a single chip can achieve all of our performance requirements (and it will be cheaper).
The 34461A’s fourth-generation multi-slope integrated ADC circuit part still uses multiple chip combinations.
EEN: We’ve noticed that in recent years, many electronic test and measurement companies have begun to talk more about applications and solutions. How should we adapt to this trend for general electronic instruments like multimeters?
WW: It’s true. For many of our products, the market requires us to adapt to more special applications, as is the case with digital multimeters. We’ve responded in several ways. Firstly, it’s very easy to add more features by upgrading the firmware. Secondly, many products can be opened to install special application functions (a bit like apps on a phone). Lastly, we’ve been working on developing more software to match the instrument to meet more unique application requirements.
EEN: What are the key technological innovations of this 3446X series multimeter compared to past products?
WW: The new digital multimeter uses a modified ADC design that allows us to achieve 7.5-digit accuracy and resolution at a lower cost and in a smaller footprint. The new generation of ADC design also enables us to achieve faster reading speeds. Additionally, we’ve added Auto Calibration (ACAL) to our equipment (34465A and 34470A) to maintain high measurement accuracy under temperature and environmental influences.
Thanks to the development of digital technology over the past 25 years, we’re able to make better use of excess computing power to do things that weren’t possible on the 34401A. We’ve ported many functions that were implemented through analog circuits to digital circuits (like calculating RMS values), resulting in higher reliability and stability, and a much cheaper price. For example, FPGAs handle a lot of tasks that used to require a dedicated chip.
EEN: The 3446X series multimeter has changed a lot in the operation interface. How do you react? What are the benefits of the new UI for users?
WW: Everyone has given very positive feedback on the new operation interface. It feels intuitive and can be used very quickly. The navigation menu makes it easy to find various functions (the 34401A panel had few buttons, so you needed complex combo buttons to navigate through layer menus to find the features you needed). Measurement results can be displayed on a larger color screen, and we can now not only provide readings but also graphically display statistical results. In UI design, we want to not only provide accurate readings but also present results in a more intuitive way, improving users’ insight into measurement results. You can now see trends, histograms, statistics, and more, not just display readings—you can analyze the data more comprehensively to better understand the measurement results.
Display test results in a histogram on a large color screen to understand distribution characteristics.
EEN: We saw a huge color screen and a new user interface on the 3446x series. In the future, are you planning to use more consumer electronics technologies like touch screens or wireless connections on desktop instruments?
WW: We will continue to research new technologies, as long as they are reliable, reasonably priced, safe, and valuable to our customers, we will consider adding them to our product design. A recent example is that we implemented the MTP protocol on the USB communication interface on the back of the instrument, so you can drag and drop data files from the instrument directly onto the PC just like a USB flash drive without writing a program.
The MTP function can directly read the test results in the multimeter memory via USB.
EEN: The reliability of the 34401A is an important factor in its success. For the new digital multimeter, what have you done with it?
WW: It’s really hard to list all the certification tests and "abuse" tests our products have undergone during development. I can only talk about them in a broader sense. It includes temperature/humidity limit testing, temperature cycling testing, mechanical abuse testing, input signal abuse testing, ESD testing, input transients and chopping testing. These are all necessary safety tests. For example, we recommend a working environment temperature between 0 and 55 ° C, but the actual ambient temperature used in the test is far beyond this range.
Additionally, you must also consider some possible misoperations, such as an engineer who didn’t sleep well the night before, accidentally loading 1000V large voltage directly into the resistance test function. Although this is a very dangerous operation, we have to guarantee it does not damage the meter.
Loading a large voltage of 1000V during the resistance test does not destroy the 34461A, but it is not encouraged to do so...
In addition, we also have the experience accumulated in the previous generation of products, this is a rich treasure house, let us refer to and learn, this information has made a great contribution to our final design decision, to ensure that we provide customers with reliable design.
EEN: Finally, what is the next product of your team? Is there a 34480A (the legendary eight and a half multimeter), or the new 34970A?
WW: Follow us, I think you will definitely like it.
The interview ends here.
Next, let’s take a look at the disassembly of the 34461A.
Look at it in the end is not reliable
The picture above is a complete disassembly of the 34461A, the process is quite tough. The most impressive thing is that there are very few screws used in the whole product (a total of only 6 screws, three of which are used to fix the fan and GPIB interface). The connection between the circuit and the housing is mainly locked by various buckles. Dead, so I was very brainburned when I disassembled the machine. Friends who like to play toys can challenge themselves with the 34461A. This design is very convenient for later installation and maintenance, and it also reduces the chance of the screw rolling into the machine to cause a short circuit.
Readers who have read the 34401A article before will find that the 34461A maintains the same design style as the 34401A, and the hardware layout is even more concise.
Top view of the 34401A
Top view of the 34461A
In the process of dismantling, the first place to get stuck is how to separate the main board from the front panel. We spent a full hour here. Finally, it was found that there is a T-shaped black buckle on the red test lead connector (below), which is the only fixing piece for connecting the front and rear panels to the main board. Just pull it out hard and you can easily remove the front and rear panels. If the clip is not removed, the front panel and the motherboard are firmly locked together.
The main board and the front and rear panels are connected without screws, but a clip is used to lock the two together.
The motherboard and front panel that were finally stripped open, the middle is the buckle
It is also worth noting that the 34461A main board and the front panel are connected by the connector inside the yellow circle of the above figure, and on the 34401A, a gray data line is additionally used. The assembly of the 34461A is obviously more convenient, just on the line.
The other time I was stuck, I wanted to see the screen control circuit of the 34461A, but I found that it could not be taken out between the two plastic structures, and there were no screws around. It was later discovered that a layer of plastic parts of the lining could be slid in parallel and then lifted up and pulled out.
Slide the upper plastic mold to the left and you can pick it up.
After the demolition, there is a thrill of great revenge!
Compared to the front panel of the 34401A in the figure below, it looks a bit thin. Also remove the two screws when removing the front panel.
Front panel of the 34401A
◠Let’s take a look at the 34461A main board that was hard to remove!
Similar to the 34401A, the 34461A’s entire multi-slope integration circuit is completely wrapped under a metal shield
There is a warning under the metal shield: Do not remove the shield, otherwise recalibrate!
Of course we will not be scared. The shield can be removed to see the complete multi-slope integration circuit. The white circular device in the lower right corner is the LM399 reference level. The main difference between the 34461A and other higher precision models is also Just in this device.
Multi-slope integration circuit seen after removing the shield
Although the six and a half multimeters are already very common, their ADCs are really sensitive, especially when the ambient temperature changes, which can have a significant impact on the measurement. This is why you should write a warning under the shield. Here we did a small experiment to measure the short-circuit voltage with the shield removed. During the measurement, we used a USB fan to align the side to start blowing.
â— Short the positive and negative ends, measure the short circuit voltage value with a multimeter
It can be seen that the result of the initial short-circuit measurement is 5.1uV. After a period of fan blows, the test result doubles to 10uV. In fact, even a person’s hand across the circuit will affect the reading. This sensitivity is really amazing, so it is easy to remove the shield.
The last one is a wounded figure, and the hand is punctured by a screwdriver.
Revenge after being abused 34461A
After the addiction, I have to reinstall the 34461A. After the self-test passed, everyone will breathe a sigh of relief and luck is not bad. Because of the past success of the 34401A, I believe that the 34461A team is also under tremendous pressure. However, we are relieved to see that the new multimeter has maintained a consistent standard from process to design. The graphical UI is also very good, both the use of new technologies, while maintaining relative restraint, taking care of the feelings of old engineers. Even for the most discerning old driver, it is very easy to get started, almost no need to turn over the manual. This is very intimate for engineers with heavy work.
How successful is this UI? As you can see from the picture below:
So this UI is also quickly borrowed by domestic manufacturers.
This one… it’s a bit bumpy…
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