[time-nuts] Part 2: Atomic Clocks: It is important that they keep good time.
Rice, Hugh (IPH Writing Systems)
hugh.rice at hp.com
Fri Jan 4 19:07:49 EST 2019
HP's Santa Clara Division (SCD), in addition to building the Cesium Beam Frequency Standard Atomic Clocks, was an official time-keeper for the U.S. Naval Observatory, maintaining the west coast reference for Coordinated Universal Time. This was done in our standards lab where we kept a rack of several HP Cesium standards. Hopefully the attached picture of the lab comes through for some of you.
A side note on the Cesium Standards in this lab. It was a collection of random instruments from over the years. The 5060 and 5061 family was reliable and easy to repair, especially with the factory was upstairs, and these were likely scrounged units of some kind. Customers also used to send Cesium Beam tubes to HP for disposal and end of life. These customer tubes were sometimes replaced on periodic maintenance schedules when used in critical applications, and often had a lot of good life left. The standards lab working with the CBT techs would pick through the returns, and select out the best tubes for the standards lab. As far as I know, the standards lab never had to purchase a new CBT. I'll bet there are a few on this list that would love to pick though the piles of old CBTs we had back in the day.
In about 1987, Jim Horner, the general manager of SCD, said: "If we keep the official time for the US Naval Observatory, we should have a fancy display in the lobby showing exact time." This would allow us to showcase our technology to customers and dignitaries that would visit the site. But there was a catch: IT MUST ALWAYS HAVE THE CORRECT TIME. (Oh, and PFS engineering needed to find the money to pay for it. But it didn't wind up being all the expensive.)
Some years prior, at HP headquarters (or maybe HP Labs?), they also had a "Lobby Clock" to show off HPs accurate time keeping technology to visitors. I never saw a picture of this it, but it was supposedly an elegant electro-mechanical clock, in a glass case so you could look in at the gold plated gears and such. On day, a visitor saw it and said: "I think your clock is slow." Impossible! It is connected to the house standard, and is *perfect*. But it was checked, and sure enough, the clock was slow by some embarrassing amount. The gold plating on the gears had gotten gummed up, and caused the clock to drag behind. Some senior executive (Packard, Hewlett, HP Labs director?) probably lost their temper, and had it quickly removed. HP didn't need an atomic clock in the lobby of the corporate headquarters with the incorrect time. (I think Lou Mueller told me this story, and most of this one is probably true. He was the lead CBT engineer, and his history with Cesium Standards went back to nearly the beginning of time. A wonderful guy that was always very kind to me, and told lots of great stories.)
This was a after the 5061B project was complete, and I was now the production engineer on the 5061B. My follies as a clock designer had not been discovered yet, and PFS management asked me to design the Lobby Clock display, and figure out a way to make sure it was never wrong. I had learned a lot about turning a 1PPS signal into a HH:MM:SS format, and leveraged this new expertise into the new lobby clock.
The strategy was to have a small clock display in the standards lab, sitting on top of the rack of official Cesium Standards, where the tech's there could regularly confirm that it indeed had the correct time. A key feature of the design was to have the 6 digits of the clock display in BCD data format, which could be piped out to the lobby on a 24 connector data cable. (I got to learn about RS 422 line drivers, which I used to drive the data lines. The distance from the standards lab to the lobby was maybe 100 feet.) The clock display in the lobby would display the BCD data, and not have to be checked, as long as the standards lab guys kept their local display accurate. No gears to gum up. What could go wrong?
The guys from the industrial design team designed a very elegant, very large black glass display for my electronics to hide behind. On the left side was an "analog clock" made of long narrow LED segments, and would progress around in a circular display with simulated hour, minutes and second hands. On the right side was a giant 7-segment, dot matrix like digital display for the time. The digits were maybe a foot tall. We had two giant PCBs laid out to hold the analog and digital clock LEDs, and all the electronics to control them. All mounted in a fancy aluminum box, with the enormous glass display over the top. It was at least 3 feet wide, and nearly as tall. And really heavy. Facilities pulled the 24 conductor cable through all the false ceilings and found AC power up there for me to plug into, and mounted the beast high on the wall in the lobby. We fired it all up, and it worked great. (Yes, I tested it extensively before we installed it.)
SCD management scheduled a grand opening ceremony for the clock display, and invited Len Cutler down to do the official unveiling. A few quick speeches, and Len pulled off the black cloth hiding it until the big event. He appeared very pleased with the product. It remained in the SCD lobby for many years, and was still there the last time I visited in the late 1990s. As far as I know, it never had the wrong time. Or at least it always showed the same time as the little, reference clock in the standards lab.
This was a really fun project, that was completed over a few months, and something that I was proud of for many years. I wonder if it is still on the wall of the lobby. Keysight technologies now occupies the building, but is no longer in the Cesium Standard business.
Have any of you ever seen this clock in the old SCD lobby, on Stevens Creek Boulevard where it crosses Lawrence Expressway in Santa Clara? Anyone know how long it was there?
Happy time keeping,
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