# Monthly Archives: September 2016

## Effect of Wire Length on Surge Protector Let-Through Voltage

While reading about how these units worked, I noticed that the amount of surge voltage they let pass (called let-through voltage) is a function of the hookup wire length. The units are tested with a hookup length of 6 inches, and the user is warned that the let-through voltage increased by ~20 V per inch of additional wire. I became curious about the origin of this rule of thumb. In this post, I will show you where this rule of thumb comes from. Continue reading

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## Video of Wild Cat in Northern Minnesota

Like me, a number of my coworkers have cabins in Northern Minnesota and most of us have cameras that record activity on our properties. A coworker came in the other day with this video that shows a wild cat going by one of his cameras. I am not sure what kind of cat it is – probably a lynx. This site is not far from the Canadian border. Maybe one of you out there can identify it? Continue reading

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## Probability That An Old President Does Not Finish Their Term

Ronald Reagan (Figure 1) was our oldest president at the time of inauguration – 69 years 349 days old. The 2016 US presidential election is giving us a choice of two candidates that will be relatively old at inauguration: Donald Trump (70 years, 220 days), and Hilary Clinton (69 years, 86 days). Since US presidents often serve 2 terms, it is conceivable they we may have a 77- to 78-year old president in 2024. This fact makes me curious as to what is the likelihood that a 70 year-old's natural life will be long enough for them to serve one or two terms. Continue reading

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## Quick Look at a High-Power PoE Graph

I have been sitting in a meeting on a high power version of Power over Ethernet (PoE) known as IEEE 802.3bt. It supports 90 W of output power with a guarantee of 71 W at the load. During the talk, Figure 1 was discussed (my version of the chart). When I am given some mathematical information, I like to experiment with it to see if I understand what I am being told. Continue reading

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## Chromatic Dispersion with 10 Gigabit Optical Transports

In this post, I will be showing how we model the effect of small amounts of dispersion as a power loss. We commonly refer to this power loss at the dispersion power penalty. I will also show how the need to limit the power penalty drives a critical laser parameter, the laser spectral width. Continue reading

Posted in Fiber Optics | 1 Comment

## Using SUMPRODUCT to Evaluate Two-Variable Polynomial

One of the most common computation tasks that my customers face is estimating battery capacity based on the battery's temperature and discharge current. Figure 1 shows a example of the capacity curves for a typical lead-acid battery. Ten years ago, I chose to implement this function with an Excel spreadsheet that used a polynomial approximation for this function. An engineer today asked me to explain how my Excel implementation works, and I felt this would be a good topic for a post. This approach is implemented using SUMPRODUCT – no helper cells were required. Continue reading

Posted in Batteries, Electronics | 2 Comments

## Open-Drain Comparator Circuit With Settable Trigger and Output Levels

Quote of the Day If you don't stick to your values when they are being tested, they're not values; they're hobbies. — Jon Stewart Introduction I received a circuit design question from a reader who was asking how to design … Continue reading

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## Janitor Math

I was working on a Saturday morning when the cleaning crew came in. On this morning, the owner of the cleaning company was with his crew. He stopped by my cube and wanted to speak for a few minutes about some cleaning issues he was seeing. His concerns centered on their increase in workload caused by a recent in the number of workers at our site. Continue reading

Posted in Daily Math | 1 Comment