Simplex Clock Correction Issues

I’m feeling a bit nostalgic this morning. Readers of a certain age will remember the classic Simplex clocks from school days. The clocks throughout the building had a special feature – a receiver and small control system that would permit the clocks to be synchronized or changed throughout the building, using a master control device. Useful to keep all the clocks at the same time, easily adjust for seasonal daylight savings time changes, and to reset the clocks in the event of power loss.

There’s a good overview of these systems here:

The Synchronous Wire system is the most popular system in the United States. Clocks are run using a power circuit that acts as its time base. The clocks receive an hourly correction which synchronizes both the minute and the second hand. Every 12 hours the clock receives a daily correction to keep the clock perfectly synchronized.

When I first started working in the medical imaging field (circa 1989), we’d run into issues with these clocks, a lot. Hospitals and health-care facilities were big users of these (there’s a clock in every patient room, hallway, and procedure room), and one particular piece of equipment (a Phillips “Classic” generator) was particularly susceptible. The generator used a motor-driven, linear variable autotransformer (think Variac or Powerstat) to adjust for line voltage changes – and the signal injected onto the mains by the clock controller (typically around 3500 Hz) would mess with the voltage regulation circuit, and the motor would “hunt” for the duration of the pulse (usually 5 or 10 seconds), The generator would be disabled or locked out while the motor was moving, and this would drive the docs and techs crazy (since it happened hourly).

Simplex Clocks

A waveform sample from a PowerLines trip report circa 2007, using Rx Monitoring Services power analyzer to capture the clock correction pulse.


I’ve also come across a few old power quality threads discussing these clock pulses causing standby / hybrid UPS systems (notoriously sensitive to anything that might indicate the start of an actual outage) to switch to inverter improperly.

Back in the day, the old BMI-4800 power analyzer had a “high frequency noise” detector which looked at broad spectrum harmonics or noise, and output a distinctive “picket fence” 24 hour log when these clocks were present (I still miss this diagnostic / reporting feature on modern power analyzers). I’m sure I have an example of this graph kicking around somewhere but can’t put my paws on it at the moment. I suspect any graphs I recall pre-date digital images (when I would create reports with blank boxes, and manually paste in photo-copied disturance graphs) so I’m not finding anything in trip reports or old PowerPoint presentations)

Resolving these issues? Sometimes we’d consult with the facility engineer – oftentimes these were turned up to “10” (maximum) and we could get the amplitude turned down to the point where it worked but did not cause problems. Sometimes we’d get the clocks reprogrammed to only correct 2x a day (noon and midnight) when it would be unlikely to affect the equipment. Some resourceful field techs developed a filter circuit to protect the regulation circuity; although that was sometimes not permitted (FDA requirements for x-ray equipment forbids modification or retro-fitting).

I don’t hear too much about these lately. Clocks are now often digital, controlled wirelessly or via ethernet. Switched-mode power converters have replaced old analog systems.


Cause and Effect: Arcing Transients and Equipment Faults

We recently reviewed some power monitor data for a client. Problem statement:

Breaker Q1 in the WCS electronic box trips on a sporadic basis. The breaker is the M4 and M5 fan motor overcurrent protection. We have replaced the breaker multiple times.

First pass, we noticed three very high current swells in the ground current data:

Ground RMS

We also saw 100s of very serious arcing voltage transients, not related to load current changes or other voltage events. The transients showed up on Phase-Neutral and Neutral-Ground, but the NG transients were much lower amplitude (secondary, not the primary issue).

Transient PhN Transient NG

Finally, we captured three current swell events that clearly show equipment faults to ground (notice the elevated ground current) immediately following voltage transients – cause and effect.

Fault1 Fault2 Fault3

Figuring out the cause of the transients is an exercise for the local service engineers or an onsite power quality engineer. But we’ve got a pretty clear linkage here between transients and equipment faults. Most of the time, power quality problems are a lot less concrete and clear.

How to Annoy Your Friendly Neighborhood Electrical Engineer

Problem Statement: A power assist chair (that we purchased for my mother back in 2016 and no longer need, looking to sell used) had an intermittent – the up/down LED lamps would go out, and the chair would not operate, until one jiggled the power cord.

Annoyance #1: Called the manufacturer to get a replacement cord (I had troubleshot it down the cord itself). Turns out the cord is hard-wired into the motor, so the solution is to replace the motor. (bad answer, the motor itself is fine). Why is a simple power cord that will invariably get a bit of wear and tear not be easily replaceable?

Annoyance #2: Yes, it’s under warranty, but it requires both a service call (to replace the motor) and shipping charges. Um, no.

Annoyance #3: Additionally troubleshot the cable and discovered the intermittent was in a little inline molded box containing an LED, the sole purpose of which (as far as I can see) is as a redundant and unnecessary troubleshooting tool – since both the chair control pendant and the transformer also have LEDs to indicate power on.

Solution: Cut the molded box LED out, strip and splice the cable (nicely soldered and insulated), it’s a wee bit kludgy with electrical tape, but perfectly safe and solid). Took about 15 minutes including time to heat up the soldering iron and then test the crap out of it afterwards.

Ultracomfort America – not impressed.

Audio Project: Buying Local vs. Amazon

I’m in the middle of a small audio project – converting 11 digital micro-cassettes (the sort used in old answering machines and personal recorders) to digital MP3 files for a client’s book / memoir project. It’s potentially slogging work (each cassette has up to 90 minutes of content, that’s up to 16.5 hours of recording) but I’ve got it set up to run in the background, while I do other things. I’m sort of embarrassed to admit that I started doing this on my computer (using Audacity sound recorder / editor) before realizing I have this perfectly good TASCAM DR-07 digital recorder (that I use for live recording) that is actually designed for this sort of thing. Using the computer would have been exceptionally onerous; the digital recorder makes it almost trivial. The only potential problem is battery life on the micro-cassette – I picked up a DC power supply but it introduced severe hum into the signal so I’m back to AAA batteries (I have a stack of those, but I imagine that the batteries will die mid-recording a few times during the process.

I’m probably over-killing the set-up here – running the 2.5mm mono output of the recorder through adapters (2.3mm -> 3.5mm -> 1/4″), then through a DI to get XLR out, and into a Mackie mixer to tweak the sound a bit (cutting out some of the highs and lows, optimizing the level) and into the recorder. I’ve got a set of headphones to listen in now and then. Next time I’m out I’m going to pick up my spare monitor speakers at my storage locker so I can have it going low in the background and lose the headphones.

Getting the adapters was 1/2 the battle here – the 2.5mm mono out is super non-standard. I went to the local Cables & Connectors store which could only supply a 2.5mm stereo, which kind of sort of worked but not really (was a little flaky) – I ended up (as always) finding exactly what I needed at Amazon (2.5mm mono to 3.5mm stereo) and while I was at it, picked up a couple of 3.5mm stereo to 1/4″ breakout cables which I seem to be wanting every other time I pull out the mixer these days (record out to the TASCAM, line out from phones and tablets). I have a bunch of 3.5mm to RCA breakouts but the 1/4 is a lot more mixer friendly.

I like to support local retail when I can, but I’m invariably looking for something a little weird or left of center and rather than drive around all day for something that almost works, just pull up the exact right item on Amazon, order via Prime, and it shows up 1-2 days later. Probably better for the environment as well (considering my gas).

Emergency Lighting & Exit Signs: Sleazy, Sloppy and Unethical

Let’s say you pull into one of those quick lube places to get an oil change. You’re not really paying attention, so you do not realize that your spouse was in there a few weeks earlier, and had gotten the oil changed. The attendant knows this (they pull up the vehicle data from the license plate or they check the little sticker, it’s been just a few hundred miles) but they say nothing – simply change the oil and send you on your way.

Would you be pissed off? I suspect the answer is yes.

Happened to my employer this week. I’ve been doing their exit sign and emergency exit testing for a few years now – a monthly quick test (push the button, works for 30 seconds, pass / fail) as well as a more involved annual test (kill the building power for 90 minutes and make sure the lighting batteries hold up). I replace the batteries and/or lighting units as needed. I last did the big annual test in July 2018, and dutifully punched out the little official stickers that I purchased to make it all official.

Exit Sign Sitcker

This week, I noticed that one of those big industrial service companies was in to inspect the fire extinguishers, and somehow convinced the facility manager that she needed an annual electrical inspection (they may have actually sold her under-coating and floor mats while they were at it). So all of my little stickers were removed, replaced with theirs, even though the stickers clearly indicated that an annual test had been done in July 2018, two months prior.

Unethical = check. Sleazy = check. And to add insult to injury, there is no way in hell they did a full 90 minute “annual test” in the time they were on site – I suspect they did a quick push-button test.  Potential criminal liability there. The funny thing is, the only reason I noticed was that they slapped the stickers on the front panel of the devices (rather than discretely along the side where my stickers were) so I spotted them as soon as I walked into the facility. So add “sloppy and lazy” to the descriptors.

We’ll be going back to them once the invoice comes in to get the charges reversed. And if that is ineffective, we’ll be sending a letter of complaint to the town fire inspector, as well as the state dept of consumer protection.

Sound Board Hacks

I’m not an audio engineer by profession, but I’ve been monkeying around with sound systems through my music career, yoga world, and tangentially though A/V freelancing for many years. So I’ve learned a few things, and figured some things out by myself. Here are a few of my favorite ways to stretch the capabilities of low end analog sound gear.

  1. Using the FX / Effects Bus as an emergency monitor bus
    Was at a band gig and the mixer board (not mine) monitor bus was not working (bad pot). Emergency fix, use the FX bus (not used by us, although some would add a bit of reverb / echo to the vocal channels) as a monitor bus. Good trick to have in the bag.
  2. Left and Right Channels feeding different sound systems
    At the big outdoor yoga class I do sound for, I feed front of house speakers, plus two time delayed satellite systems. Since we’re mixing mono, I just pan everything to center, use the left channel for front of house, and the right channel for rear of house (mixer → delay → mixer + amp → delay → amp) for the 2nd and 3rd speakers. That way I can tweak the level of the remote systems from the main board without having to schlep 200 feet down the road to the second mixer / amp.
  3. Monitor Channel as Talkback Channel
    Same outdoor yoga gig. I transitioned the musicians (an electronic / percussion / world music group) to headsets instead of monitors (they tend to move mics around and stuff, a real feedback nightmare in previous years). Last year, I set up my own headset / mic (using a gamer headset) and sent the headset audio only to the monitor channel, giving me the ability to talk to the band during the gig. Similarly, I set them up with a talkback mix that they could communicate with me (to set levels, etc.)  Super handy when setting levels and during the class.

Power Factor Correction Capacitors on a Timer

Came across an old friend this afternoon, low frequency transients related to utility or facility power factor capacitor switching, controlled via a timer (rather than sensing voltage, current, or power factor)

Minor PFC - Voltage Waveform

Here’s the voltage waveform – this seems to be a very minor transient, hardly worth noticing.

Minor PFC - Voltage and Current Waveform

Adding the current, we see a small ringing current related to the transient event. Oftentimes with more severe transients we see a large current swell.

Minor PFC - RMS Logs

The RMS voltage logs show a small but clear step increase in voltage at the time of the transient, clear sign of power factor correction capacitor switching.

Minor PFC - Table of Events

Finally, here is a table of all such transients captured. Notice how each transient occurs at 7:03 am, on different mornings. This sort of “same time every day” incident is a clear indication that the capacitor bank is on a timer control.

Not a super serious issue, this time, but interesting to come across a timer based system. They seem to be increasingly rare as more sophisticated controllers are brought online each year.

Power Standards Lab: Announcing: The PQube 3 Family

Came over the email transom this week:

We are pleased to let you know that we announced the commercial availability of two new PQube® 3 models.The range of PQube 3 analyzers now includes:

  • PQube 3 – ultra-precisee multi-function and multiple-circuit power quality and energy meter. Ideal for immediate diagnosis of power issues, power consumption analysis, as well as environmental sensing, and external process monitoring
  • PQube 3e – multi-load powerr consumption monitoring for 14 single-phase loads, or 4 three-phase loads measured simultaneously; drastically lowering the per-circuit cost of monitoring
  • PQube 3v – voltage quallity analyzer; ideal for price-sensitive applications where compliance is required, while load monitoring is not

Features of the PQube 3 analyzers include:

  • Ultra-compact form factor; fits virtually anywhere – ideal for embedding (DIN-rail)
  • Detection and recording of high-frequency impulses at 4 MHz
  • Measurement of 2 kHz – 150 kHz emissions (first instrument on the market to cover the entire frequency range)
  • Four analog and multiple current channels (up to 14 on PQube 3e)

Benefits of using the PQube 3 analyzers include:

  • No learning curve – very intuitive, with no software needed
  • PQube 3 generates information you can immediately use – disturbance and trend graphs sent directly to your iinbox
  • Additional channels and embedded sensors provide a precise set of measurements covering the power side, plus process monitoring, and environmental parameters
  • Measurements can be used for verification requirements; PQube 3 is certified Class A IEC 61000-4-30 Ed3, and is ANSI Class 0.2/0.2S revenue-grade accurate
  • Optional enterprise software enables fleet maintenance and data aggregation

Read the full press release here.

I’ve been a fan of PSL Founder Alex McEachern from back in the BMI days; have not had a lot of opportunity to work with the PSL devices / technology. To be honest, without an on-staff or on-call power guru (like me) to help sort out signal from noise, the technology seems a little hard to use / parse for the layperson. But cool as hell, from a power quality perspective….

Backups and Archives

We’re in the process of re-organizing our office back-ups and archives.

For a while now, we’ve had a 1TB D-Link mini-server, dual parallel drives, serving as a backup device. It’s been getting full – so we decided to review and revamp. Turns out a big chunk of that drive (700 GB, at the moment) is devoted to one client, and an archive of site data and reports that go back nearly 15 years. In the early days the data sets were relatively small (by today’s standards) – 10 or 20 MB maximum. But today, we regularly see data sets that exceed 1GB.

So, new plan, we picked up a relatively low cost, 4TB backup drive (USB connection) and are moving all of the customer data over there. There’s no real requirement for this data to be backed up permanently, it’s more of a “nice to hang on to” archive. That way, we can free up the 1TB drive (still nicely serviceble and redundant as an automated backup device) for everything else.

What this requires, however, is patience. In the process of copying 700GB of data from the network drive to the USB drive is taking some time (days really); it’s slowing down my main workstation a bit but not enough for me to set up something else to handle the chore.

Once the data gets pushed to the new drive, I’ll clean up the old backup drive, and also clear out some space on my main workstation and spend some time defragging the disks.


RIP: MCM Electronics

From the ARRL Website (9/21/17):

MCM Electronics, in business for 40 years, will close two plants and its corporate headquarters in Ohio and lay off more than 90 workers, the Dayton Daily News reported earlier this summer. The company, which carries an electronics inventory of more than 300,000 items, including 3-D printers, tools, wire, cable, and other items, has been a Dayton Hamvention® vendor.

The layoffs will begin at month’s end and continue through the end of the year.

You can now find the MCM Electronics catalog on the site:

MCM Electronics and Newark element14 have partnered together for over 32 years as part of the Premier Farnell family. Now, MCM will be strengthening this partnership under the Newark name. MCM’s unique product offering combined with Newark’s vast inventory, expanded services and global reach makes us the one stop shop for engineers, installers, educators and makers.

MCM Electronics and I go back a long ways. I’m pretty sure my first purchase was a set of Spin Tite nut drivers; I’d found them super handy in the labs at my first job at Superior Electric and soon after purchasing my first home I outfitted a workbench. Still have that small set of color-coded, english gauged drivers. Over the years I bought oddball tools and test equipment, parts and components, and most recently audio-video equipment. I’ve got a storage locker full of A/V gack: LED Par Lamps; speakers, speaker stands, lighting stands, lighting truss, XLR and speaker cables. Often purchased via one of the seemingly insane 50% off sales that would periodically flood my physical mailbox. MCM Electronics seemed to be one of the last bastions of physical catalogs; I still have their last catalog on my shelf.

Why yes, I did buy four of the 12″ PA speakers at $44.99 each…

It was never the highest quality stuff, but it was light duty, serviceable, good enough for my needs.And for whatever reason, their shipping department seemed to be amazingly responsive – I’d order stuff “slow boat” and it would show up 1-2 days later; big boxes of speakers or truss or whatever.

And while stuff still seems to be available, I have no doubt that the selection will narrow, the catalogs will stop coming, the to good to be true sales prices that often enticed me to buy will no longer be offered.

End of an era. There’s a lot of that going ’round in my world these days….