In early 2005, I was handed a project by Dr. Clement Burns of the Solid State Lab.  He needed:

A high vacuum a system that utilizes a rotary vane vacuum pump as well as a turbo molecular vacuum pump. This system needs to be automated to simplify operation and to protect the delicate turbo pump. In order to protect the turbo pump a system should designed that would automatically isolate the turbo pump in case of an unexpected increase in pressure. This system needs to provide a vacuum pressure in the low ranges of 10^-5 Torr which is in the high vacuum range.

Thankfully, I did not have to work alone on this project.  I was teamed with Dan Adams, a graduate student studying Solid State Matter, who handled all of the mechanical needs for the project, including assembly of the cart and all mechanical aspects.  Dan also had an opportunity to assist on some of the electronic controls that I designed, built, and implemented. 

To make a cart like this seemed like it would be easy.  Plumb two pumps together, a couple of switches, a couple of relays, and bada-bing, we have a vacu-cart.  It didn't end up working out quite that quickly or simply, since we had not seen or used a vacu-cart before and only had a concept in our head as to how it would work. 

The logic of the cart was handled using a 40-pin Basic Stamp Module (BS2P40).  It can manually open and close each of the three valves, turn on and off the backing pump and turbo pump, reads two thermocouple gauges and displays the output on the LCD.  In addition to the manual mode, there is also an "Auto" mode which will open all valves and start the backing pump.  Once a rough vacuum has been achieved, valve 3 will close, and the turbo pump will start.  If at any time the vacuum begins to fail by either gauge, valves 1 and 2 will close and the turbo pump will be shut off.  Other safety features include the turbo pump not being available to turn on until a rough vacuum is achieved.

The code for the BS2P40 can be seen here.

The Vacu-Cart in action during the LiNH3 Conductivity Experiment

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