Hi
I bought mass flow controller rated for hydrogen gas 1 to 5 sccm. Got the wiring diagram from from site (attached) now I made another diagram to control the the gas flow through 10k variable resistor. As in the picture. On my voltage meter I see 0 voltage, even when change the resistance. What could be the issue in my modified circuit?

 

Zero volts where? From what two points, in what conditions.

Does the voltage change on pins 6 and 8 when the pot knob is turned. Unless the shutoff valve is open and there is pressure on the inlet, the flow value voltage will and should read zero even with a flow command voltage.

 

Zero volts where? From what two points, in what conditions.

0 volts on the display

 

0 volts on the display

Edited my comments above. Does your display show voltage on the input pins 6 and 8 when connected there?

 

Edited my comments above. Does your display show voltage on the input pins 6 and 8 when connected there?

The display is conected to pin 2 and 7, theoretical i should be able to control the flow 1 to 5 volts = 1sccm to 5sccm throw pin 6 and 8 as in the picture

 

The display is conected to pin 2 and 7, theoretical i should be able to control the flow 1 to 5 volts = 1sccm to 5sccm throw pin 6 and 8 as in the picture

Did you test for correct voltage at the input pins? Do you have gas pressure on the inlet and is the shutoff valve opened?

 

Did you test for correct voltage at the input pins? Do you have gas pressure on the inlet and is the shutoff valve opened?

No. i didn't try with gas. Going to test today maybe this is the reason. But over all is there something wrong with the 2 diagram with the display?

 

No. i didn't try with gas. Going to test today maybe this is the reason. But over all is there something wrong with the 2 diagram with the display?

Not that I can tell, but I have no idea what MFC you are using. They are pretty simple interfaces on the old analog units.
https://mfchelp.com/mass-flow-controller-tutorial/connector-types/
I have a few that I used to make a fire demo with propane.


https://www.artisantg.com/info/Horiba_Stec_SEC_4400MC_Datasheet_2017101795254.pdf

It's a Mass Flow Controller with a set-point, feedback from flow to set-point. That means there are two functions inside, one for control (5V input controls a flow valve to set gas flow) and one for measurement (5V output the movement of gas in/out of the MFC). With no gas you get zero flow for measurement and zero volt read-back. That's a good thing.

 

Not that I can tell, but I have no idea what MFC you are using. They are pretty simple interfaces on the old analog units.
https://mfchelp.com/mass-flow-controller-tutorial/connector-types/
I have a few that I used to make a fire demo with propane.
View attachment 350004
View attachment 350007
https://www.artisantg.com/info/Horiba_Stec_SEC_4400MC_Datasheet_2017101795254.pdf

It's a Mass Flow Controller with a set-point, feedback from flow to set-point. That means there are two functions inside, one for control (5V input controls a flow valve to set gas flow) and one for measurement (5V output the movement of gas in/out of the MFC). With no gas you get zero flow for measurement and zero volt read-back. That's a good thing.

I'm using horiba stec 7330m 1 to 5 sccm h2 gas.

 

I'm using horiba stec 7330m 1 to 5 sccm h2 gas.

A good MTC. We're using mainly the new digital programming and interface models on new gear.

Be careful, H2 flames are hard to see and have a wide explosion mixture range with air.
https://h2tools.org/bestpractices/l...y-operations/hydrogen-hazards/hydrogen-flames

 

Did you test for correct voltage at the input pins? Do you have gas pressure on the inlet and is the shutoff valve opened?

Tha gas is the salvation. . It worked now. I cantrol the gas flow with the variable resistor. Thanks

 

Tha gas is the salvation. . It worked now. I cantrol the gas flow with the variable resistor. Thanks

Just be sure to close the shutoff valve first and adjust the flow to full when shutting down gas flows so there's no trapped gas behind the flow control value.

 

Just be sure to close the shutoff valve first and adjust the flow to full when shutting down gas flows so there's no trapped gas behind the flow control value.

No worries ,this for high vacuum project.

 

A good MTC. We're using mainly the new digital programming and interface models on new gear.

Be careful, H2 flames are hard to see and have a wide explosion mixture range with air.
https://h2tools.org/bestpractices/l...y-operations/hydrogen-hazards/hydrogen-flames

View attachment 350024
View attachment 350026

My project is fire free just partical. I made the controller compact for my project

 

No worries ,this for high vacuum project.

I work with UHV equipment with lots of flammable and toxic gasses. Gas leaks happen on everything and H2 loves to leak at every sealing surface. All it takes is a static spark to start a fire that you can't even see. Be pro-reactive.

 

I work with UHV equipment with lots of flammable and toxic gasses. Gas leaks happen on everything and H2 loves to leak at every sealing surface. All it takes is a static spark to start a fire that you can't even see. Be pro-reactive.

Thanks for the warning and I will try my best not to blow up my house. If that happened and my house exploded, you all have to know that I love you all. Thanks every one for the help.