MKS 901p

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Finn Hammer
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Re: MKS 901p

Post by Finn Hammer »

All,
The 901P transducers are plentiful and cheap on Ebay right now, and I have been working with them the last month or so.
Bruce Meager's post on interfacing with RS232 was most helpful to me, since this is the first time I have used that interface.

I am using an Arduino to query the 901P about the present pressure, a small Oled to display the answer, and the code is very simple.
I am a hardware guy, not a programmer, so it can probably be made a lot fancier, but it seems to work so far, so what.....
Code at the end of this post.
Arduino breadboard with MAX3232 and MKS901P. Also the small A Nano which will be the final target for the code.
Arduino breadboard with MAX3232 and MKS901P. Also the small A Nano which will be the final target for the code.
A couble of warnings:
The TTL signal from the Arduino needs to be translated to RS232, and this is done by a MAX3232 chip. I did not know this at first and it cost me the RS232 functionality of a 901P, which stopped responding after it was connected to TTL RX/TX.
(Why a +-10V interface caves in @0-5V is beyond me)
Another thing, the Arduino becomes unresponsive to program upload when the MAX3232 is connected to the RX/TX ports, so you should disconnect it when you upload the code to the Arduino.

I intend to wrap the Oled, the Arduino into a small enclosure with the connector at the bottom, and a Lipo battery with associated charger/booster to form a compact transportable unit.
This is the pressure gauge to bring with you, when you go out to buy a new foreline pump.
Mounted in a fusor, the 3 built in relays with programmeable trip points could come in handy, for example, disable/enable power to diff/turbo pump at say 35 Microns. Operate the foreline vent to atmosphere valve and foreline valve, in the case of a power failure.
I have tested the code with a 999 Quattro and it works there as well.

The code:
-------------------------------------------------
//This program queries MKS 901P and 999 series pressure transducers about pressure, and displays the result on small Oled display.
// 09-09-2017 Finn Hammer


#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);

String sensorValue;

void setup()
{
Wire.begin();

display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // initialize with the I2C addr 0x3C (for the 128x32)(initializing the display)
Serial.begin(9600);

}
void displayPressure() {

Serial.print ("@254PR3?;FF");
sensorValue = Serial.readString();
sensorValue.remove(0, 7); //Remove the forst 7 caracters from @253ACK7.39E+2;FF to get 7.39E+2;FF
sensorValue.remove(7); //Remove caracters from the 7th, to get 7.39E+2

display.clearDisplay();
display.setTextColor(WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.print("Foreline Pressure");
display.setTextSize(2);
display.setCursor(0, 12);
display.print(sensorValue);
display.setTextSize(1);
display.setCursor(98, 25);
display.print("Torr");

}
void loop()
{
displayPressure();
display.display();
}
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Richard Hull
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Re: MKS 901p

Post by Richard Hull »

Great work Finn! This will help a number of folks here provided they have soldering skills and are willing to work with the Arduino.

I have been doing this for a few years now. (Arduino inclusion in projects)

I develop with the UNO as you did here, using a breadboard and wires all over the bench to finalize and de-bug a proposed design. In the final iteration I tend to use the Arduino Pro-Mini as it is half the price of the Nano which has the USB port on it. To program and re-program the Mini you need an FDTI dongle. The Pro-Mini is better if you are making a distributed product as folks are not tempted to plug a USB cable into your distributed device. However, I agree that for a personal, portable item, the Nano is a better choice since you, as the originator, can re-program with no hassles.

I have been building a number of Geiger counters since 2014 with the Arduino pro-mini as the core item. The kits I made just did not sell well, even among the the ham radio enthusiasts! A lot of these folks don't do any electronic work, (soldering, construction, etc.) A constant complaint is "I don't have time to build a kit"....."If you had one assembled, I might be interested." I now only offer assembled items at 3X the price and they sell OK now.

There are still electronic builders and enthusiasts out there, but the old original, "hands-on" cadre of ham radio folks are no longer major electronics "doers" due to modern ready to run ham gear.

Richard Hul
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Silviu Tamasdan
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Re: MKS 901p

Post by Silviu Tamasdan »

Actually I am still building my radio gear - I have to admit it, sometimes from kits. :)

Silviu
-KC1BJW
There _is_ madness to my method.
John Futter
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Re: MKS 901p

Post by John Futter »

Silviu
Yes some of us still put stuff together
see my QRZ.com page (ZL2TUD).
And yes it is in operation for the last three weeks.
Jerry Biehler
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Re: MKS 901p

Post by Jerry Biehler »

I think the basic arduino uses a usb-serial chip on the same serial port as what you are tying to use. I dont know if there are any other serial ports on that arduino but the higher end ones have multiple serial ports and real usb so you dont have to worry about this problem.
Silviu Tamasdan
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Re: MKS 901p

Post by Silviu Tamasdan »

John Futter wrote:Silviu
Yes some of us still put stuff together
see my QRZ.com page (ZL2TUD).
And yes it is in operation for the last three weeks.
(nice - I'm at the opposite end of the power spectrum; mostly QRSS, my most powerful transmitter is 200mW)

I also like the Arduino Pro Minis - especially the 3V versions. You can embed them in very small projects and power from a tiny LiPO battery - for instance in the payload of a model rocket.
There _is_ madness to my method.
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Finn Hammer
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Re: MKS 901p

Post by Finn Hammer »

All,

The first version of my code had a couple of shortcomings, which has now been ironed out.
Firstly, it did not comply with the fu-speak pressure unit system. fu-speak?? Confused?, well so was I.
Pressure units were never easy, and the world has odd preferences when it comes to expressing the value of a pressure. In Asia they favour the Pascal (or so I read), and so does the scientific community. Europeans are fond of the Millibar. Yankees swear by the torr.
And then there is that weird little group of fanatics "The Fusioneers" (and the associated group of wannabees), they have their own silly system. A system based on torr, which is the unit down to 1.0E-00, where it changes to the micron, which must be religiously adhered to all the way to 1.0 E-03 torr (0 Microns) where the unit changes again, this time to millitorr.
In appreciation of the immense work given here by mr. Hull, (who is a stern advocate of the micron), and with a nod to a certain mr. Orwell, I call this system for fu-speak, short for fusor-speak.
It only took 25 extra lines of code to comply with fu-speak, it was a fun coding exercise, and besides, I have pledged to use the micron around fusion pressures and generally gotten used to it, so here you have it.
However, it would also be nice to be able to display the pressure in Pascal, since it is so highly touted in the scientific community, and in all the books. And as an educational feature, switch back and forth, to perhaps gain a working ability to switch between units without having to grab a calculator, and/or swear in dispair.
Of course, you could go with HectoPascal and learn to multiply with 1.33 but.....
Anyway, I needed an excuse to learn how to implement the Interrupt routine in programs, so I took this opportunity do use the response to the activation of two switches, to toggle betweeen two branches of the program.
One where the transducer is first prompted to answer in Pascal, the other to report back with the pressure in torr.
This works nicely, and I am satisfied, (as in proud), of my acheivement.
The outputs looke like this now, just a push of a button apart:
Pressure displayed in fu-speak
Pressure displayed in fu-speak
Pressure in proper Pascal
Pressure in proper Pascal
The can of worms approach has to stop, and I have already ordered d-sub receptacles to solder to a motherboard which will form a mechanical backbone for, and harness the arduino nano, the battery charger/boost converter and the MAX232 RS232 to TTL converter, the two switches, a power switch, the battery and the display.
I will also try to find a suitable (as in available) box to wrap up the whole caboodle.
The code needs small adjustments to the placing of the units, for example, millitorr should start further to the left, when this is done and has been tested with a diff-pump, the code will get it's V.1.00 stamp, and I will write a nice little post, with all details needed to replicate the work, in the case that you should want to.

Meanwhile, you can grab the code here:


//VacuuMeter V.0.9
//This program queries MKS 901P and 999 series pressure transducers about pressure,
//either in torr or pascal, and displays the result on small Oled display.
// 27-09-2017 Finn Hammer


#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);
String sensorValue;
String pressureUnit;
String unitBuffer;
String unit;
const byte ledPin = 13;
const byte interruptPin3 = 3;
const byte interruptPin2 = 2;


void setup() {
display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // initialize with the I2C addr 0x3C (initializing the display)
Serial.begin(9600);
pinMode(ledPin, OUTPUT);
pinMode(interruptPin3, INPUT_PULLUP);
pinMode(interruptPin2, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(interruptPin3), pascalISP, FALLING);
attachInterrupt(digitalPinToInterrupt(interruptPin2), fuspeakISP, FALLING);
}


void loop() {
if (unit == "Pascal") {
pascal();
}

else if (unit == "Fuspeak") {
fuspeak();
}

display.display();
}


void pascalISP() {
unit = "Pascal";
Serial.print ("@253U!PASCAL;FF");
}


void fuspeakISP() {
unit = "Fuspeak";
Serial.print ("@253U!TORR;FF");
}


void pascal () {
Serial.print ("@254PR3?;FF");
sensorValue = Serial.readString();
sensorValue.remove(0, 7); //Remove the first 7 caracters from @253ACK7.61E+2;FF to get 7.39E+2;FF
sensorValue.remove(7); //Remove caracters from the 7th, to get 7.61E+2}
pressureUnit = "Pascal";
display.clearDisplay();
display.setTextColor(WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.print("Foreline Pressure");
display.setTextSize(2);
display.setCursor(0, 9);
display.print(sensorValue);
display.setTextSize(1);
display.setCursor(85, 25);
display.print(pressureUnit);
}


void fuspeak () {
Serial.print ("@254PR3?;FF");
sensorValue = Serial.readString();
sensorValue.remove(0, 7); //Remove the first 7 caracters from @253ACK7.61E+2;FF to get 7.39E+2;FF
sensorValue.remove(7); //Remove caracters from the 7th, to get 7.61E+2

unitBuffer = sensorValue;
unitBuffer.remove (0, 5);
if (unitBuffer == "+2") {
pressureUnit = "torr";
}
else if (unitBuffer == "+1") {
pressureUnit = "torr";
}
else if (unitBuffer == "+0") {
pressureUnit = "torr";
}
else if (unitBuffer == "-1") {
pressureUnit = "micron";
sensorValue.remove (1, 1);
sensorValue.remove (3);
}
else if (unitBuffer == "-2") {
pressureUnit = "micron";
sensorValue.remove (1, 1);
sensorValue.remove (2);
}

else if (unitBuffer == "-3") {
pressureUnit = "micron";
sensorValue.remove (1, 1);
sensorValue.remove (1);
}
else if (unitBuffer == "-4") {
pressureUnit = "millitorr";
}
else if (unitBuffer == "-5") {
pressureUnit = "millitorr";
}
else if (unitBuffer == "-6") {
pressureUnit = "millitorr";

}
else pressureUnit = "endelse";


display.clearDisplay();
display.setTextColor(WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.print("Foreline Pressure");
display.setTextSize(2);
display.setCursor(0, 9);
display.print(sensorValue);
display.setTextSize(1);
display.setCursor(85, 25);
display.print(pressureUnit);
}

Cheers, Finn Hammer
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Richard Hull
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Re: MKS 901p

Post by Richard Hull »

Finn,

You have every right to be very proud of your work. What ever unit works for any particular person is fine, of course. The units I use are still used by amateur and many professional vacuum heads here in the U.S. As noted before, why I use the micron at all is that virtually 100% of all surplus TC gauges are in microns. All working fusor pressures are in microns, as you note. However for the "deep pumpers", (folks who go sub-micron), they have gauges pretty much set up in Scientific notation Torr units. (again surplus gauges). Naturally if you purchase a current $1500.00 sub-micron baratron and its extra $500.00 controller you can digitally select your favorite unit as all are included, much as you have done in your arduino software.

100% of all scientifc literature is in S.I. by codified law within the properly annointed in academia.

Great work with the arduino. I have yet to apply it to the fusor as I, currently, have all older stock electronic instrumentation that already reads out digitally using old school electronics. I assembled my system before there was a workable arduino and from older gear I have hand on hand since the 70's. (nim counters, digital counters, digital pressure gauges, etc. Virtually all use TTL or older MSI logic chips and nothing uses a microprocessor or micro-controller in the fusor IV system.

If some key chunk of fusor IV digital apparatus dies, I'll probably do up an Arduino kluge as a new replacement.

Again, great effort and work.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Pablo Llaguno
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Re: MKS 901p

Post by Pablo Llaguno »

Finn,

Great and impressive work! What you are doing was the exact same plan I had from the beggining, minus the Pascal conversion which is a nice feature. However school hasn’t given me the time to work with the arduino serial communication, I actually bought a rs232-TTL converter that already has the dsub-9 head, but I couldn’t get the arduino to transmit/receive anything from it. When I get it working I’ll post my results, and maybe I will borrow some of your code :)

Thanks for the post,
Pablo
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Finn Hammer
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Re: MKS 901p

Post by Finn Hammer »

Pablo, Richard

Thank you for your kind words.
I am using this little rs232/ttl converter board:

https://m.ebay.com/itm/5PCS-Mini-RS232- ... Ciid%253A1

It is a bit finnicky to work with, due to the size, but otherwise it is fine. It has to be unplugged from the Arduino while you upload code.
Also notice that the code does not do a Pascal _conversion_, rather it instructs the 901p to respond in Pascal, as you can see in the Pascal ISP:

void pascalISP() {
unit = "Pascal";
Serial.print ("@253U!PASCAL;FF");
}

Cheers, Finn Hammer
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Rich Feldman
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Re: MKS 901p

Post by Rich Feldman »

Very late to this party, I just powered up my first MKS 901P. LED comes on red, then changes to green.

Analog output is +9.45 V whether at atmosphere, or me sucking on the hose, or connected to a vacuum spigot on the wall here.
My guess is that the analog output mode is not at factory default state, it's set to emulate some other transducer model that's pegged at full scale for my three test points.

Sounds like RS-232 communication is needed before more progress.

Did confirm that 901P connector pin 1, which they call Transmit, is putting out -4.5 V. That's a normal RS-232 level, as the device Marks time. :-)
I think it corresponds to RxD in a traditional modem connection. Signal direction is from the DCE device (modem) to the DTE device (terminal, computer, or USB converter). It's called RD at both ends. Would be on pin 2 of a DE9 connector at both ends, right? Thanks!
All models are wrong; some models are useful. -- George Box
Rex Allers
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Re: MKS 901p

Post by Rex Allers »

The LED action you describe is correct.

You didn't actually tell us what pins on the 901p connector you are measuring for the analog.

I have gotten three of these. They all have the 3-row 15-pin D connector (like VGA monitors use). I assume yours does too. I haven't seen one yet that wasn't set up to all defaults when I got it. If yours has been set to some other analog output curve, you'll need to get the serial connection working to issue status read commands or to change a setting. (I assume you knew that.)

Here's a pic of the circuit for an adapter that I wired up to connect to the 901p.
901P my cable.png
The top two parts are straight out of the manual. Just to be clear, the left pic of the 15-pin connector is looking into the connector on the sensor. I wired it up just like their picture on the right. For power, I connect to a small 12 V SLA battery (12V 7Ah) and I have a switch in the (+) line so I can turn it on and off.

The list at the bottom probably only applies to what I did. I found a VGA cable and cut off one connector so I had a cable with wires on one end to a female 15-pin that plug into the 901p. The colors are what I learned about the cable after ohming all the pins. On a VGA, pin 9 isn't needed so there's no wire for that. I haven't used the sensor relays yet but I figure the Normally Closed of relay 1 I can probably live without.

Here's a pic of the little board I made for this.
Adapter detail.jpg
For the two pins I provided to measure analog out, they are just like in the circuit diagram, the (+) goes to the 901p pin 5, and the minus to pin 6.

I don't usually use the analog out, but I tried it tonight. I connected a DVM. At atmospheric I saw 8.88 V. On a pump, the serial measurement output said 2 E-2 (20 mTorr) and the voltage was 4.3 V, which matches the default chart in the manual.

To see how your 901p is configured or to change it you'll need to get the serial interface talking. I checked the connections on my adapter board. On the board I've got a 9-pin female connector that plugs into the 9-pin male on the end of a USB-to-Serial adapter cable I am using. So the pins on the female 9-pin of my adapter are wired just as shown. (Pin 1 of the 901p 15-pin is wired to pin 2 of the female 9-pin on my adapter.)

The command to check the analog output emulation is:
@254AO1?;FF
(254 is a broadcast address so should always work.)

Mine returns:
@253ACK30;FF

So is set to '30' which is the factory default.
Rex Allers
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Rich Feldman
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Re: MKS 901p

Post by Rich Feldman »

Yay! One MKS901P is all better now, after some hand-typed serial communication using Tera Term. That users-manual figure copied by Rex resolves, on close inspection, the proper TD and RD connection to RS-232 port with a DE-9 connector. A voltmeter gave the same answer: when unconnected, each device's serial output line presents a negative voltage.
DSCN0664.JPG
The magic kiss was to send the command @253FD!ALL;FF (restore factory defaults) at 9600 baud. Then the device became communicative. The non-default setting with which it was received is gone for good.

A trial command, @253TST!ON;FF, made the green LED start blinking as expected.

Some ID and status queries were unsurprising, with one exception.
DT? "LOADLOCK"
MD? "901P"
TEM? "2.93E+1" (degrees C)
T? "O" (both sensors are OK)
BD? "NAK160". (What's up with that? Expected to see the baud setting.)

OK, time to read atmospheric pressure.
PR3? "7.61E+2"
PR4? "7.611E+2" (new challenge: how repeatable and continuous is the significand's fourth digit, in a device with FSR of eight decades? )

Analog voltage output was now 8.88 V, right where it should be. Got it down to 8.62 V (around 400 torr) by mouth sucking. (Probably not the wisest experiment, but the KF-16 flange looked pretty clean, and didn't taste so bad.) Missing is my other MKS901P, already plumbed up to a hose that will fit mechanical vacuum spigots at work.

Thanks for the original tip, and development help!
All models are wrong; some models are useful. -- George Box
Pablo Llaguno
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Re: MKS 901p

Post by Pablo Llaguno »

You are not the first to try to see if the transducer works by mouth sucking, a very sophisticated method indeed :D
Bruce Meagher
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Re: MKS 901p

Post by Bruce Meagher »

Rich, try BR? not BD? to get the baud rate.
Ameen Aydan
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Re: MKS 901p

Post by Ameen Aydan »

Hello,

I am very bad at anything that comes to computer programing so I apologize if I sound very inexperienced. I remember Andrew Seltzman posting code on this thread. He said that it is possible to use Matlab as a program to properly interpret the signals. I'm imagining that you use the analog output then hook it up with an Arduino that changes it to a language that the computer can understand. Then, you use the Matlab software that has Andrews code written into it and allow it to display the pressure reading. Is this how you would go about using Matlab as a programming platform? Or more importantly, is this what Andrew did when he used Matlab?

I hope this is a good approach to the general direction of being able to read the pressure off an MKS 901p. Is there anything I have gotten wrong? I would really love to know how to program this to use it but I really don't have that much time in my hands right now.

thank you
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Rich Feldman
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Re: MKS 901p

Post by Rich Feldman »

New chapter & question (near bottom) in my tale of two MKS 901P's. Both procured via ebay some time last summer, and talked about here.

Unit 1 (s/n ending with 2835): Bad start. Plumbed it up and saw analog V_out = +9.45 V with no vacuum. Had previous user programmed it to emulate a different device?

Unit 2 (s/n ending with 3803) was first to meet a serial port & terminal program here, because Unit 1 and the KF adapters had been misplaced. This beginner needed a couple of tries to establish interactive communication, including a "restore factory defaults" command which might not have been necessary. Then Unit 2 gave sensible pressure readings and analog output levels for two pressure cases: atmosphere and mouth sucking.

Soon Unit 1 and the plumbing turned up, but six months passed before another serial port session (today).
Now I think Unit 1 might be really broken.
Serial communication worked from the get-go. Baud rate query "BR?" returned 9600. Hourmeter "TIM?" returned 6360.
Transducer status "T?" returned O (both sections OK)
Analog output "AO1?" returned 30 (factory default log function)
but
Pressure reading "PR3?" returned 2.86E+3 torr
Measured voltage was still +9.4 volts.
Those didn't change after factory defaults command "FD!ALL".
Anybody out there familiar with this kind of misbehavior?

Back to Unit 2. "TIM?" 5010 hours. "PR3?" 7.61E+2 torr. Analog V_out = 8.9 volts.
Now it's connected to a facility vacuum port at work, and V_out has been creeping. I observed 7.4 to 7.6 volts (25 to 39 torr), corresponding to sucking power of about 28.9 to 28.3 inches of Hg. A voltage logger is keeping it company for the night.
All models are wrong; some models are useful. -- George Box
Bruce Meagher
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Re: MKS 901p

Post by Bruce Meagher »

Rich,

I don’t have any insight into your broken 901p, but can you dump of all the parameters? Cut and paste the following commands into your favorite terminal program when you’re connected to the device.

@254PR1?;FF
@254PR2?;FF
@254PR3?;FF
@254PR4?;FF
@254BR?;FF
@254AD?;FF
@254RSD?;FF
@254MD?;FF
@254PN?;FF
@254DT?;FF
@254MF?;FF
@254HV?;FF
@254FV?;FF
@254SN?;FF
@254SW?;FF
@254TIM?;FF
@254TEM?;FF
@254UT?;FF
@254T?;FF
@254U?;FF
@254GT?;FF
@254VAC?;FF
@254ATM?;FF
@254AO1?;FF
@254AO2?;FF

These devices are easy to disassemble, and o-rings are used for sealing. Maybe take yours apart and see if there is any visible corrosion. Below is a pic of one dissembled. Remove the two bolts next to the rs-232 connector then press the two retaining pins on the side to remove the shell. The top board is just held on by the connectors. The bottom board with the two sensors is connected by 4 screws. The piezo sensor is visible on the bottom but the pirani is feed by the little tube and the guts are hidden from inspection. I believe this particular pirani sensor is described in patent US5557972A https://patents.google.com/patent/US5557972A/en

Bruce
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Last edited by Bruce Meagher on Mon May 18, 2020 1:58 pm, edited 2 times in total.
Chris Giles
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Re: MKS 901p

Post by Chris Giles »

Rich Feldman wrote: Mon Jul 09, 2018 7:35 pmBD? "NAK160". (What's up with that? Expected to see the baud setting.)
In case anyone else sees similar, the manual says:
The following list provides descriptions of the NAK codes that may be returned.
NAK Code Error description Example
8 Zero adjustment at too high pressure @253VAC!;FF
9 Atmospheric adjustment at too low pressure @253ATM!7.60;FF
160 Unrecognized message @253S%;FF
169 Invalid argument @253EN1!of;FF
172 Value out of range @253SP1!5.00E+9;FF
175 Command/query character invalid @253FV!;FF
180 Not in setup mode (locked)
...
If the transducer is supplied as a special version (P/N: 901P-xxxxx-xxxx) with pre-configured parameters such as setpoint settings, the setup is per default locked. The transducer will reply with error code “NAK180” if the user tries to change parameters. To change pre-configured parameters refer to unlock procedure page 21.
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