The Project Blog

Let’s take it apart

SMC ZSE40-T1-22L Digital Pressure Switch

February27

ZSE40eBay is my vice. At some point I knew I was going to need some sort of vacuum gauge better than the tiny scale on the bottom end of my suction-side HVAC gauge. I’d looked at your standard bourdon type gauge, but to get accuracy beyond 3% put me in the $50 price range. Then I came across a ZSE4 on eBay.

The ZSE4, it turns out, had been discontinued. I’m not so much a fan of most discontinued stuff, so I went to SMC’s website and scoped out their other offerings. The ZSE40 line was the replacement for the ZSE4 and looked exactly like what I wanted.

Vacuum measurement, though, is an odd beast. This gauge measures kilopascals (kPa). In the realm of science, 0kPa is absolute vacuum. The datasheet for this gauge says it reads down to -101.3kPa. What now? How can I have less than absolute vacuum?

What the datasheet doesn’t say is that it measures gauge pressure, not absolute pressure. Gauge pressure is referenced to atmospheric pressure while absolute pressure is referenced to an absolute vacuum. Atmospheric pressure is 101.3kPa and thus a -101.3 reading on the gauge correlates to absolute vacuum. Hurray.

It also has two built-in switches with individually assignable set-points. The units of measurement can also be changed to inches of inHg, mmHg, PSI, and bar. Accuracy is stated to be ±2% full scale ±1 digit or less.

I didn’t look around to see what the retail price was on one of these guys before I bought it, but I did when I got around to writing this entry. Allied is selling this guy for $124. I paid, shipping included, $43.

posted under Equipment

Email will not be published

Website example

Your Comment: