MKS 901p vacuum gauges

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Bruce Meagher
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MKS 901p vacuum gauges

Post by Bruce Meagher » Fri May 18, 2018 9:57 pm

A bunch of MKS 901p vacuum gauges recently showed up on eBay. I’d recommend grabbing one, or a few, for your vacuum projects. Unlike the thermocouple gauges these don’t require a special controller. A simple 15V power supply and a PC / Mac is all you need (or one of Finn’s beautiful controllers). Also these are dual pirani / piezo gauges so they give a reasonably accurate pressure reading from atmosphere all the way down to sub-micron (perfect for a fusor). Just make sure you get the -11040 version that has the RS-232 interface.

I was able to get a few at $35 each with free shipping. ... 2129!US!-1


Chris Mullins
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Re: MKS 901p vacuum gauges

Post by Chris Mullins » Fri May 18, 2018 11:26 pm

I can second the vote for the MKS 901p. I just use the analog voltage output, which is conveniently a log output - 10^(x-6) = torr, where x is the analog voltage out.

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Samuel Berman
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Re: MKS 901p vacuum gauges

Post by Samuel Berman » Sat May 19, 2018 12:47 am

I just got one for $30! Make sure to use the make offer feature to get a lower price.
"You miss 100% of the shots you don't make."

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Rich Feldman
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Re: MKS 901p vacuum gauges

Post by Rich Feldman » Thu Jun 07, 2018 7:13 am

Thanks for the tip. I got a couple and am eager to try 'em out.

Might even skip finding a mating D-sub connector (DE-15 HD), and use a few individual pin receptacles.

Looks like only 4 wires are needed, to use analog voltage out. Would that depend on mode settings in nonvolatile storage, only changeable by digital commands?

Or for RS-232 access only, 4 or 5 wires including power. I'm pretty rusty with RS-232. Can anyone here recommend a terminal emulator program or other application software? How about getting RS-232 connectivity on a Windows PC with no classic "serial" port?
Richard Feldman

Andrew Seltzman
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Re: MKS 901p vacuum gauges

Post by Andrew Seltzman » Thu Jun 07, 2018 12:37 pm

Teraterm is a good terminal program, use a USB-serial adapter if you don't have a port. The DB15HD is just a VGA style connector, they are really easy to get.
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John Futter
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Re: MKS 901p vacuum gauges

Post by John Futter » Thu Jun 07, 2018 7:04 pm

Teraterm is good as is putty

Rex Allers
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Re: MKS 901p vacuum gauges

Post by Rex Allers » Fri Jun 08, 2018 12:21 am

A long time back, in another MKS 901p thread, a member was looking for serial software. I did some browsing for ideal software that ran on multiple platforms and had a way to save and call back canned communication strings. I found one I wasn't aware of before called ScriptCommunicator:
or ... l-terminal

It is relased under the GNU General Public License version 3.0 (GPLv3)

It seemed to have a very powerful scripting language built in and had versions for Win, Mac, and Linux. It took a while for me to begin but I wrote scripts for it to control and read the 901p. There are two levels of scripting in SC:
1) One for sending simple command strings, but with the option to add pull-downs to customize. I used that feature for the command to set the unit (Torr, Pa, etc).

2) A very powerful kind of script where you can do things like open your own custom user interface GUI window for a function. I used this to read and display pressure from the 901p every second.

Here's two captures of that interface as it starts, and reading.
Read_901 Dialog 2.png
901p and SC windows
That was at atmospheric. Here's a capture from the 901p on my Welch pump.
Welch 20 min.png
Reading Welch pump
Welch 20 min.png (11.05 KiB) Viewed 1292 times
So I got most of what I wanted working around Sept 2017 and I really like what can be done with this program. I wanted to share my scripts for talking with the 901p but every time I started and I realized all the aspects I would have to explain, I found sharing would be more work than the coding I had done. Here are some details why.

1) ScriptCommunicator has a pdf manual but it is a bit terse in many user interface details. I thought I would have to describe a lot of details for those who would like to configure and use what I had done.

2) Each OS environment has some differences, like where all the files should be. I have used Windows on XP through Win8.1. I have zipped all my add-on scripts but there is a lot to describe about where to put them and how to get them configured in SC to use them. I did try one Linux machine and got it working there but I had some permission issues that I probably didn't get past in the best way. I don't use *nix much. I don't have any Apple PCs so someone else would probably have to work all that out.

3) To connect the 901p through the serial port I hand-wired an adapter. It was a little board that feeds a cable to the 901p 15-pin connector. The board supplies DC power to the 901p and has a 9-pin connector to accept (usually) a USB to Serial adapter. I also have two pins to monitor the analog output signal from the 901p, but haven't used that much. All of this is not too very complicated but needs more description.

4) I probably should document a bit about the scripts I have done and how to use them although I hope they are mostly self explanitory once they are installed correctly. At some point it would be good to describe more about this powerful scripting language and how I used it.

5) I think I could add a feature where the pressure readings and time-stamps are optionally saved in a file. I did a little looking at scripting calls to do that but the task never got near the top of my list.

So... I've been meaning to share this way to use the MKS 901p for the better part of a year. Each time I started I fizzled as I saw the amount of work to describe all the details.

Are there many of you who would like to use this stuff? If I heard enough interest maybe I would be encouraged to do more work on sharing.

Anyone out there who would be willing to help documenting in any way? I guess the first step would be having the ability to design and build your own interface board / connectors, and get the 901p talking to the serial terminal of your choice. I could begin aiding that process by writing a description of what I did to make my hand-wired interface. Then maybe I could talk someone through ScriptCommunicator and my add-ons by email and/or phone to begin initial sharing.
Rex Allers

Jerry Biehler
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Re: MKS 901p vacuum gauges

Post by Jerry Biehler » Fri Jun 08, 2018 6:33 am

I use RealTerm, probably the best terminal for techies out there that I have found. All sorts of cool options.

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