Solenoid Valve Operation

What make of solenoid valve, and part number?

Its not specific to any particular make or model

Then neither can the responses be to this posting. If the valve is power one way, spring return, then a two-pulse digital output is not applicable, irrespective of what has been read.

OK, you don't know what kind of a solenoid you need to control. Do you know what kind of digital output is available in this control room and how far away is the solenoid?

Your question is way too generic to be answered without pure guessing--

My guess is the pulsing originates in the Software of the controller that writes to the digital output. Check the controller software, somewhere around line 1432, or perhaps another line of code may be doing it.

The solenoid valve (I guess that is what u r referring to as SOV) is based on the electromagnetic principle.

You may refer to Solenoid in wikipedia or many other places to understand the exact working.

In simple terms,

• Consider a spoon inside a cup.
• The spoon is free to move in the cup.
• To move the spoon a force is required.
• Consider the Cup to be the static electromagnetic winding.
• Consider the spoon to be a ferrous(iron) spoon (or of any material influenced by magnetic lines of force), this is called the armature(moving part)
• When an electrical voltage is applied on the stator//static electromagnetic winding - the cup. A magnetic force is induced which pulls the spoon (ferrous//iron armature) to itself.
• When you do not apply the voltage the spoon is not attracted by the cup.

This is a very simple explanation.Now consider that the armature is held away using a spring, Position A.When u apply voltage the spring force is countered by the electromagnetic force and the armature is pulled towards the coil. when the voltage is released the electromagnetic effect dies down and the spring force draws the armature away.To hold the armature from going out of bounds, a restricting member may be in place.
To answer ur question:Depending on the armature and spring arrangement the arrangements differ and so do the type of solenoids..eg: push type, pull type, push-pull type(two sets of coils) with a neutral central allign position.Except for the pushpull type, for all types of solenoids one control signal is sufficient.eg: '1' is Active (push or pull), '0' is inactive state or default state.And the hardware needs to be designed to interpret the signal to the desired voltage state to apply to the solenoid.
The solenoid can be used to activate many things by having the armature open and close pneumatic or hydraulic valves or cause mechanical motions.
For ur reference I am including a few links:

1. http://www.solenoid-valve-info.com/solenoid-valve-basics.html
2. http://en.wikipedia.org/wiki/Solenoid_valve
3. http://www.howstuffworks.com/electromagnet.htm
4. http://en.wikipedia.org/wiki/Electromagnet

regards,Vishal....

Most solenoid valves are based on a simple electromagnet concept in that when power is applied the valve is held in one position. Generally a spring will return the valve to the other position.

There have been solenoids made that have the ability to latch in one position, held by a permanent magnet, and then driven the opposite direction with a reversal of the applied voltage or a second coil. These are special purpose devices and are probably not what you encountered.

In general, the valve you mentioned will be operated by a control system. The control system has instructions for when and how long to hold that valve open or closed. You will have to investigate the control system to understand the why and how for each device.

There is usually no need for two pulses except as a method of flow control or dosing. Since every system is unique, there are no general rules for how they are used.

True, but if the equipment the control system is operating is a little older, he could have a ratchet relay on the solenoid end applying the power. This would enable a pulse on, pulse off control.

That's one idea. Another idea is that the solenoid is wired to a web page capable programmable logic controller. All they have to do in the control room is call up the correct IP address and turn the correct bit on with their digital control. Then again the digital control could be the original digits found on the human hand. The solenoid is wired into a pull chain socket and a string has been run through pulleys into the control room.

Even if we guess the correct digital control configuration I doubt the OP will tell us we guessed correctly.

Inputs & Outputs could be in the form of Analog or Digital.

Analog : 4~20mA, 1~5Vdc, 0~10Vdc, pulse, discreet(off, on)

Digital : Ethernet, Modbus, Profibus, HART,...etc.

In order to process and control these data, you need to have some Central Processing Unit or Controller that will somehow convert Inputs to your desired outputs.

Simpler to view:

INPUTS>CPU OR CONTROLLER/CONDITIONER/CONVERTER>OUTPUTS

In your case:

PULSE> CONTROLLER/CONVERTER/MODULE> DISCREET (ON/OFF) SOLENOID

Anyway: PULSE is not digital signal

If power consumption is a significant concern, you may consider to use a latching solenoid - requires power only to switch, not continually.

Google same - they may provide application notes -

Hi,

The working principle of the SOV has been well described above. I believe you are looking for how it is wired from the system. The DO terminals of the system is connected to the field IO cards also known as FTA's. Both of these are powered 24V DC. In the program logic, when a DO signal is activated, a 24V appears at the output terminals of that particular channel to which it is connected. Field final control elements like the SOV are not directly connected to the system terminals. The are mostly connected to FTA's or Field Terminal Assemblies which have relays installed on them to isolate the system from the field. This is just a protective measure to safeguard the systems. So now your SOV can be 24V, 110V or 240 V depending upon your requirements. The SOV will be connected to the NO/ NC terminals of the relay and the relay coil is actually connected to DO terminals of the system.

So now when the signal is activated, 24V comes at the system terminals which in turn powers the coil of the relay. This latches the NO/NC terminals. You can connect your required power supply to these contacts to activate the SOV.

Hope this helps...

Yes I wanted to know how it is connected to system. Ok now once solenoid valve is energized, and now I need to de energize it as per my process requirement. Relay contact is latched. Now how to unlatch it? Only one digital output is consideres for solenoid valve, then what triggers relay to unlatch? Is it theo logic?

There are many ways to do it.

The simplest way is that the relay/SOV is latched(active) as long as the signal is high('1') and the relay/SOV is unlatched(deactivated or at rest) if the signal changes to low('0'). Also the analog circuit may be designed to interpret PWM frequencies(to avoid confsion in a noisy environment) or to detect the rising and falling edges or may be given explecit commands over I2C or Serial or differential line signals... There is no end to the possibility of the methods of providing the activating or deactivating signal. It boils down to the hardware(the control circuit//the analog circuit//the SOV) and the design specifications.

regards,

Vishal

Now to deactivate the sov, you or the software logic will have to produce a logic 0 at the system output for that particular channel to which the SOV is connected. So, when there is a '0' at the system out, the 24 V required to energise the relay is lost and the relay output becomes zero. This breaks the supply voltage to the sov and hence it is un-latched.

Now, how the zero comes to the system out is a part of logic. You can go through the ladder logic and determine what all conditions must be fulfilled in order for the SOV to latch. Just reverse any of the process parameter and the SOV will be unlatched. First, I suggent you go through the entire logic sequence and be aware of what you are going to do. Because, there may be other references to the SOV in another part of the logic. You don't want to trip the entire plant... do you...

All the best..

It also depends on the type of logic used or the communication protocol(if applicable).

I think MSN should provide more info to help everyone help MSN ;)

I re-read ur question.

As said earlier most solenoids just require 1 control input, only special case u require 2 control signals.

The 1 pulse or two pulse is a little vague...

And for "who gives the pulse?" the answer is simple,, the Digital control circuit or card or however u like to name it. The Digital signal is provided to a circuit which on application of the signal or a pulse of signals would provide the analog voltage required by the SOV. (how the circuit is designed and what analog circuitry is implemented, what voltage SOVs are used, and the distance of the control circuit from the analog control circuit and the distance from the analog control circuit to the actual SOV and other factors determine the type of digital signal or sequence of digital signals required. I guess that would betoo vast to discuss on a vague idea.)

I guess rather than how the SOVs work u wanted to know how the digital signal is interpreted. I am in the Embedded domain and hardly ever used PLCs. I dont know what u r familiar with. The way things are implemented differ but the underlying system is the same. My explaination is based on my working with micro-controllers and drive systems.

take care...

Vishal...

As already mentioned there are many types of solenoid valves. With a spring return valve one output will work. But in order to know how energizing or de-energizing is achieved you need to know what type of solenoid valve you have. Even air piloted valves may or may not have spring return actuators. So in order to answer your question maybe you should research what you are asking first.

redfred is actually correct in many respects!

The controller - dependant upon some factor(s) can trigger the pulse for the SOV. The pulse is sent from the controller to the SOV - or SOV interface to operate the SOV.

Now getting it to actually work is an entirely different conversation - where as the "digital output" is not enough to trigger the SOV, and therefore needs some type of interface logic to actually make the SOV work properly. Other comments from above also apply.

I might have got idea about the solenoid valve operation.

Let me tell you about the energizing & de-energizing operation of the SOV.

For this operation, you need a PLC. And in that a DO & two internal timers are needed.

First trigger Ist timer directly, then trigger IInd timer through the pulse of Ist timer and then at the end connect it's O/P to Do. Again reset the Ist timer by IInd timers pulse. Adjust timings as per your requirement.

You have to develop logic in the PLC by this control philosophy.