Auto-Sampler Timing Circuit

Swatsell

I currently have an system that performs auto-sampling of plastic pellets. Every 30 seconds, a valve is opened for 5 seconds. This releases the pellets from the process line to a container.

I'm using a GE Fanuc PLC for this and would like to replace it. The cost of a PLC for such a simple circuit seems a bit ridiculous.

My question is: What type of microprocessor should I use, and, will the output handle the load of a approximately 1/2 amp?

Thank you,
Jerry

Phil Pilgrim (PhiPi)

You don't mention whether the load is AC or DC, or what voltage.

-Phil

Mike Green

A Prop-1 will do the job and has Darlington drivers included on the board that can handle 1/2A DC.
See: www.efx-tek.com/topics/prop-1.html.

Shawn Lowe

Well, if it has to be PLC like try this:

http://www.parallax.com/detail.asp?product_id=30064

Otherwise, any of the basic stamps will work, with some modifications. Maybe not even that much work.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Shawn Lowe


Maybe I should have waited to do that......

Swatsell

The end result is to power a 120 VAC solenoid that will switch a diverter valve. What I need to know is how to go about getting a contact closure that will open/close the circuit to the solenoid (or relay).

Mike Green

The RC-4 will switch 120VAC (see: www.efx-tek.com/topics/rc-4.html). It has some additional circuitry on it that you don't need, but it is laid out for use with 120VAC and it will work with the Prop-1. You could use the Prop-1 to drive other solid state relays as well if you want to do your own layout.

Phil Pilgrim (PhiPi)

The Prop-1 device that Mike mentioned, plus an RC-4 Relay Control Board and a solid state relay should handle the job. There are some caveats on the product page regarding the ULN2803A that I'm not sure will affect you. Perhaps Jon Williams can join the discussion to clarify and to help pick the appropriate parts. The goal, of course is to keep the overall cost below $100, since that's where PLC pricing kicks in.

-Phil

Unsoundcode

Hi Swatsell, a BS2 should handle your application. There are inputs you could use to say enable or disable sampling or to indicate when the machinery is running or stopped. Relays can be switched from the outputs via a transistor circuit. If the 30/5 second timing is not absolutly critical you could control the valve action with Pause statements.

The attachment is an example of transistor control, replace the motor in the schematic with a relay.

Jeff T.