Relay to Energize Solenoid
Eugene
Posts: 7
Hello Everyone,
I am a Basic Stamp Newbee. I am very much interested in microprocessor process control, and have purchased a BS2 and have been experimenting with it in my spare time.
I would like to apply what little knowledge that I have regarding microprocessors to opportunities at my business. I have a hydraulic press used to mark parts. It is currently controlled manually. I would like to use the Stamp to query two non-tie down switches during the operating cycle (the cycle stops if either switch is not pressed- safety issue). Also, I would like to have the cylinder return automatically, likely using a pressure switch. The cylinder would stop with the assistance of a proximity switch, and both non tie-down switches would have to return to their Normally Open state for a period of time (while another part is being loaded) before it could be recycled.
The extension and retraction of the cylinder is controlled by a solenoid operated directional control valve. The solenoids that are currently on the valve are 110VAC and draw 1.6 A peak.
My main question is what type of relay would be preferred for the Stamp to energize the solenoids? I believe that I can use certain solid state relays directly with an output pin on the Stamp (for example, Jameco P/N 176698CM has a very low input current). Would there be any advantage to using an electro-mechanical relay? The output current on the Stamp is insufficient to trip this type of relay directly, so I presume I would need to use a transistor as a switch. From my perspective, this adds to the complexity. I also have an option to change the solenoid coils to 12 VDC. Would this be preferable?
Any input that can be given to relieve my ignorance will be most appreciated.
I am a Basic Stamp Newbee. I am very much interested in microprocessor process control, and have purchased a BS2 and have been experimenting with it in my spare time.
I would like to apply what little knowledge that I have regarding microprocessors to opportunities at my business. I have a hydraulic press used to mark parts. It is currently controlled manually. I would like to use the Stamp to query two non-tie down switches during the operating cycle (the cycle stops if either switch is not pressed- safety issue). Also, I would like to have the cylinder return automatically, likely using a pressure switch. The cylinder would stop with the assistance of a proximity switch, and both non tie-down switches would have to return to their Normally Open state for a period of time (while another part is being loaded) before it could be recycled.
The extension and retraction of the cylinder is controlled by a solenoid operated directional control valve. The solenoids that are currently on the valve are 110VAC and draw 1.6 A peak.
My main question is what type of relay would be preferred for the Stamp to energize the solenoids? I believe that I can use certain solid state relays directly with an output pin on the Stamp (for example, Jameco P/N 176698CM has a very low input current). Would there be any advantage to using an electro-mechanical relay? The output current on the Stamp is insufficient to trip this type of relay directly, so I presume I would need to use a transistor as a switch. From my perspective, this adds to the complexity. I also have an option to change the solenoid coils to 12 VDC. Would this be preferable?
Any input that can be given to relieve my ignorance will be most appreciated.
Comments
You're headed on the right track, just as you are. For an industrial environment an SSR (solid state relay) is a fine choice. Choose an SSR with a 5 volt or logic level input. Otherwise you'll need an interposing transistor or second relay.
As far as your safety control switches and proximity switches are concerned, so long as you're just looking at NO or NC contact closures, you'll have no problem "reading" them with the Stamp.
If I missed any important questions, just shout back.
Regards,
Bruce Bates
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I suspect you know this, but for anyone that is reading and thinking about doing the same......
The safety control switches are OSHA requirements. Hopefully if you are over-riding there features, the machine will be dedicated to automatic feed. Otherwise, you leave yourself open to litigation from employee injuries.
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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
I use BS2's for industrial control all the time. I have a PC board I designed that has 16 SS I/O modules on it.·It uses Input or Output modules.
Grayhill makes a Mini line of Modules and they interface directly to the stamp I/O pins. Digikey carries them. 70M-IAC-5 is the AC input, and 70M-OAC-5 is the AC output. The Output Module·can handle 24 to 220 VAC at·3 Amps. If you think the Solenoid load is too much then put a bigger AC Relay on the output of the SSR. The pull in time will be insugnificant when compared to the Solenoid pull in time and hydraulic activity.
The SSIO modules need a pull up resistor when connected to the Stamp I/O pin. I use an LED and 480 ohm resistor as a pullup for the SSIO's. It limits the current the Stamp Pin must sink to a safe level.
I would keep the 120 VAC Solenoids. They are already there, and easier to use in an·industrial environment than· 12 DC.
You can then keep the 120 volt AC switch circuitry intact and read them with the stamp. The less you rewire a safety type circuit, the better off you are.
Always have an Emergency Stop Circuit that Works even if the Stamp is fried. It is OK to have the Stamp allow the machine to turn on, but it must be able to turn off no mater what the failure is in the stamp. The National Electrical Code requires an E-Stop Button that can break a circuit even if the contacts are welded shut. If you rewire any part of that circuit you must conform to it. All the Emergency Stop Operators (Fancy name for push button switch) made now a days are this type. They have no spring activated contacts. Mashing the button pushes the contacts apart with a rigid actuator.
Is this a completly hydraulic press or a good old fly-wheel type? Some of the older flywheel types do not lend themselvs to electric control.
Hope this helps with some of your questions.
Alan Bradford
Plasma Technologies
www.plasmatechnologies.com
Mr. Bradford, it is completely hydraulic.