A heart rate monitor is used in sports and fitness to measure your heart rate in beats per minute. It is useful because you can calculate your maximum heart rate pretty accurately from your age, and with that know your % max heart rate at any time during your fitness activity.
Over the years exercise physiologists have been able to calculate “heart rate zones” for people to keep their HR within during exercise. So for instance, if you want to increase your aerobic fitness you keep your HR between 65 and 80% of your max HR. 80 – 90% is anaerobic fitness. And above 90% is to increase your lactate threshold. Essentially a heart rate monitor allows you to train without risking over training.
Before we get to how they work, let me tell you that their are a lot of companies that offer great monitors these days. Modern monitors are worn as watches and most require you to also wear a belt like band around your rib cage just below your chest. Garmin HRMs are the brand that offers the best watches with built in GPS tracking and Polar watches are the brand that offers the most choice and also (probably) the best value for the money.
Actually a heart rate monitor is pretty simple. The chest band has an electrode and an antennae (modern ones use bluetooth wavelength) that measure your hearts changing voltage patterns as it beats… And talks with the software/computer within the watch on your wrist… It uses its internal software/computer (in the watch) to calculate to beats per minute. It then displays it for you to see. Pretty simple, hey?
You buy a monitor based on how you train – running, cycling or general fitness seems to be the types most commonly offered.
Here is a good resource walking you through the specific heart rate monitors for each style: Heart rate monitor reviews. I recommend heading to the ‘Best of’ page’.
A pressure washer is actually a pretty simple device – a motor to power a pump, really. How it all fits together, maximising low cost and high quality and being effective at cleaning are some of the design constraints for a power washer. Engineering really is just balancing a few factors, and with pressure cleaners, there is no change. Here I’d simply like to take a look at a few different kinds of them so that we can have a think about the how and why each is the way it is.
There’s really only 2 types: electric and gasoline powered pressure washers (side note: check out some in depth pressure washer reviews). Electric ones with an electric motor and gasoline use a combustion engine. The electric ones tend to be cheaper and smaller and less powerful and the gasoline ones more expensive and bigger in all ways…
…So why? The answer is that the electric motors available to power the pump are smaller, cheaper and yet less powerful than the gasoline pressure washer engines. There seems to be a turning point at around 2500PSI water pressure, where you stop seeing electric ones and only see gas ones. So obviously the engineers saw that it was actually cheaper to switch to gasoline power at around this pressure to keep the price relative.
If they’d kept making the electric ones and fitting them out with bigger and bigger electric motors to provide the pressure – the price, size and weight would all blow out and it would stop making sense when compared to gasoline power.