Stevens Chart Recorders

Stevens Chart Recorders
Got an email from my old employer - Stevens Water Monitoring Systems, Inc. announcing the last build of their chart recorders. Chart recorders were the mainstay of their business for most of the last century, but electronical gizmos are pushing them off the stage.

Drawing of complete chart recorder

These old chart recorders were little marvels of mechanical engineering. The pen moves back and forth, driven by a wheel connected to a float. The paper is driven by a clockwork mechanism that only needed to be wound every six months, when the USGS field guy came by to change the paper. It was conceptually simple, but there are hundreds of little details that made the machine reliable and effective. They are also expensive. I think they cost something like five or ten thousand dollars.

The have been mostly replaced by electronic sensors, electronic data loggers, like the DOT Logger, and radios, like the GHT. Loggers and radios are fairly commonplace these days, but the sensors are still something of a black art. Mostly they use water pressure, and when you want to know the level of a body of water to within an inch, your pressure sensitivity needs to be very high. One inch of water spread over ten square miles of lake is a stink load of water.