Controlling 8-Pin Relays With Proximity Switches

From your narrative is sounds as if you are controlling the relay with a start (NO/momentary) and stop (NC/momentary) switches. The prox switches are controlling the solenoids - this latching relay is replacing a simple on/off maintained switch (toggle switch) with a Push-To-Start and Push-To-Stop scheme.

Is this correct?

Thanks for your response.... I have determined there is no need for a start switch, the system could start by simply providing positive or negative to the coil in relay controlled through a toggle as you said. The prox limit switches control the relays which provide the required amperage to the forward- reverse solenoid valve. The push to start and push to stop complicate things needlessly I am now thinking.��

Here is a crude drawing of how it can be done. Sorry I don't have a drawing program on this computer.

Here's what I understand: The hydraulic solenoid directs fluid one way when energized and the other way when de-energized. Is this correct? (I am assuming so).

I am assuming that the limit switches are momentary.

I'm thinking that you need two latches, one to control the current through the solenoid (latching one of the limit switches) and the other to latch the start switch.

Your 8 pin relay, I believe is a double throw, double pole relay, but with only one coil it can only create one latch.

You need two 5 pin relays (Single pole double throw).

Here is a drawing of a relay latch circuit. When Sw1 is closed, the relay energizes and holds itself energized through the contacts CT1. When Sw2 is opened, the relay releases.

If my understanding of your circuit is correct, you need two of these latches. One is for the Start and Stop buttons. When you push the Start button (Sw1), the circuit has to stay energized until you push the Stop button (Sw2). This latch powers the rest of the circuit (the second latch, hydraulic solenoid, and limit switches) from the hot side of the relay.

The second latch is for the limit switches. (I am assuming that the limit switches are momentary acting.)

For the sake of argument, I am assuming that an energized solenoid directs the cylinder to the right, and de-energized to the left. In this case, the normally open contacts of the left limit switch would be Sw1. When the cylinder is full left, Sw1 closes momentarily energizing the hydraulic solenoid and the relay (which remains latched), and the cylinder moves to the right.

When the cylinder reaches the right limit switch, Sw2, the normally closed contacts open and break the circuit to the relay and solenoid. The solenoid is now de-energized and the cylinder moves to the left.

I hope this helps.

A latch would typically be needed to keep a coil energized, but why would one be needed to keep a coil deenergized? It seems that one four-pin relay (SPNO) would be enough; or is something wrong with post 2?

I made a few assumptions:

• The limit switches are momentary with NO and NC contacts
• The hydraulic solenoid is energized to direct the cylinder one way and de-energized to direct it in the other direction

The Start - Stop circuit is fairly straightforward. A relay latches to keep it on after the Start button is pushed and released. Pushing the Stop button (normally closed) opens the circuit and releases the relay.

If the limit switches are momentary (my assumption), then a second latch is needed to keep the solenoid energized for cylinder travel in one direction. This circuit is just like the first one, only the limit switches take the place of "Start" and "Stop".

You have two different functions here, and I don't see how one relay can accomplish that.

As I said, this is all based on my understanding of the OP's intended circuit.

Presuming that de energized is the retracted position,put the retracted limit switch in parallel with the start switch,and the extended limit switch in series with the stop switch.

When the cylinder extends,it will break the latch circuit,causing the cylinder to retract.

When it hits the retract switch, it will re-energize the start/latch circuit.

Use one set of contacts to latch the relay,and the other set to energize the coil in the extended position.

Remember: All start switches in parallel,all stop switches in series.

Sorry,no schematic,but I hope my explanation is sufficient.

Here's how you can get the latch:

The switches are momentary contact.

If you require "no volt protection" then what you want to do can't be achieved with just one relay.

If, however you don't need no volt protection, then replace the on/off push buttons with a simple SPST switch, and it can then be done with one relay.

The attached circuit should assist.

A slightly revised version of my first circuit that disconnects supply from both sides of solenoid when switch is off.

If the solenoid should require a reversed polarity to the proximity switches, then simply move the On/off switch to the other supply leg as shown below

I am overwhelmed by the responses, thank you all. In answer to your questions.... The prox switches are momentary. The hydraulic solenoid requires energizing on both forward and reverse cycles. The momentary starting switch is not a must, but it does need a stop switch.

There are two coils on the solenoid valve, one for in stroke, one for out stroke

Then simply fit a latching emergency stop button in series with the on/off switch in my circuit

I suggest that you use a single-coil 4way solenoid valve,similar to an ASCO:

http://www.asco.com/en-us/Pages/solenoid-valves.aspx

This will simplify wiring,reduce energy consumption and improve reliability,and give fail-safe operation in the retracted position in case of a power failure.

I would do this with an arduino and a couple of Opto22 solid-state relays. I did this with a waste water tank transfer setup that was started by one switch and turned off by another.

As long as we are not building a polar bear trap.