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atucker4072 17-02-2014 00:00
Magnetic Read Switches
 
We just found out that we have to use the magnetic read switches. How so we use them and how do we program for them? Are there any documents already out there on the subject?

xXhunter47Xx 17-02-2014 00:10
Re: Magnetic Read Switches
 
Quote:
Originally Posted by atucker4072 (Post 1344292)
We just found out that we have to use the magnetic read switches. How so we use them and how do we program for them? Are there any documents already out there on the subject?
What make/model are the switches? What compiler are you using?

atucker4072 17-02-2014 00:16
Re: Magnetic Read Switches
 
Quote:
Originally Posted by xXhunter47Xx (Post 1344298)
What make/model are the switches? What compiler are you using?
I was just about to edit it to say we are using labview. it says mrs- .087 -b

Alan Anderson 17-02-2014 00:21
Re: Magnetic Read Switches
 
A typical magnetic reed switch is treated just like any other contact closure sensor. It gets wired between the SIG and (-) pins of a Digital Input, typically the white and black wires of a servo extension ("PWM") cable. In LabVIEW, it is a Digital Input. The value returned by the DIO Get function will be True when the contact is open, and False when the contact is closed.

atucker4072 17-02-2014 00:29
Re: Magnetic Read Switches
 
Quote:
Originally Posted by Alan Anderson (Post 1344305)
A typical magnetic reed switch is treated just like any other contact closure sensor. It gets wired between the SIG and (-) pins of a Digital Input, typically the white and black wires of a servo extension ("PWM") cable. In LabVIEW, it is a Digital Input. The value returned by the DIO Get function will be True when the contact is open, and False when the contact is closed.
And to use this to stop the cylinder at a certain point you would just stop the flow to the cylinder?

novamx3 17-02-2014 00:41
You can't use them to stop the stroke at a point... They are strictly for sensing when the cylinder has reached it's end of stroke (or a given point but the cylinder will still continue onto the end of stroke unless it has flow controls and is limited to a very slow travel rate.). Almost all pneumatic cylinders have 2 positions and 2 positions only (typically extended or retracted). If we could use hydraulics we would be talking about lvdts and proportional controls... Alas, it is against the rules!

juchong 17-02-2014 00:55
Re: Magnetic Read Switches
 
Quote:
Originally Posted by novamx3 (Post 1344313)
You can't use them to stop the stroke at a point... They are strictly for sensing when the cylinder has reached it's end of stroke (or a given point but the cylinder will still continue onto the end of stroke unless it has flow controls and is limited to a very slow travel rate.). Almost all pneumatic cylinders have 2 positions and 2 positions only (typically extended or retracted). If we could use hydraulics we would be talking about lvdts and proportional controls... Alas, it is against the rules!
As nova stated above, these switches are only to be used to check whether a cylinder is in a certain state. This might be useful for things like: "Is the loader inside the frame?", "Is our launcher completely reset?", etc. Some of that feedback can let the cRio know if you're in a state that's ready to shoot, possibly keeping you from dry-firing.

atucker4072 17-02-2014 01:12
Re: Magnetic Read Switches
 
Quote:
Originally Posted by novamx3 (Post 1344313)
You can't use them to stop the stroke at a point... They are strictly for sensing when the cylinder has reached it's end of stroke (or a given point but the cylinder will still continue onto the end of stroke unless it has flow controls and is limited to a very slow travel rate.). Almost all pneumatic cylinders have 2 positions and 2 positions only (typically extended or retracted). If we could use hydraulics we would be talking about lvdts and proportional controls... Alas, it is against the rules!
So you could control the position as long as the flow is at a very slow rate?

Doc Wu 17-02-2014 09:38
Re: Magnetic Read Switches
 
No, that's not how pneumatics work. Even if you shut off the air supply at the solenoid, the air trapped will continue to expand. The only thing that stops a pneumatic cylinder is a physical stop: the end of the cylinder or a mechanical limit.

There is a common misconception that switches, or any sensor, 'stop' machinery. I used to get this in my profession all the time, even from engineers. Sensors do not stop anything. They do not have magical powers. All they do is report on the condition they were installed for. They are feedback, not action. I've seen many expensive electronic switches destroyed in machinery because someone designed them to stop the travel of a mechanical piece and put them in the path of that piece.

Also, it's a REED switch. If you ever opened one up, or looked at a bare one, you'd know why. Two thin, flat ferrous metal blades are trapped in a glass tube with the ends overlapping, but not quite touching. When a surrounding magnetic field induces a magnetic field in the blades, they attract to each other and close the gap. Simple and effective.

atucker4072 17-02-2014 10:15
Re: Magnetic Read Switches
 
Alright thank you for the help! I have never worked with the pneumatics before.


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