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Normally Open and Normally Closed
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Robert W Greif
Posted 7/3/2011 08:03 (#1846345)
Subject: Normally Open and Normally Closed



Dallas Center IA 515-720-2463
Bobby is confussed.
Normally Open and Normally Closed.

Is? On the Deere switch in the photo below,
With the planter lowered, and the button on the switch is not against the plate. The switch is on [electric currect passing thru switch]
With the planter raised, the button on the switch is depressed. The switch is off [ no currect thru the switch]

I am thinking that is Normally Open.
Right or wrong?

Also a Electric Solenoid Hydraulic Valve,
No currect to the valve, means no hydraulic flow.
With currect to the valve, there is hydraulic flow.

Is that Normally Closed.

In other words:
Does Normally Open mean - If nothing is happing to make the deal work, as button pushed, wisker pushed, or electric currect, the switch is OFF.

In the picture the planter is raised and the switch is off.



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tedbear
Posted 7/3/2011 08:25 (#1846377 - in reply to #1846345)
Subject: RE: Normally Open and Normally Closed


Southern Minnesota Between Freeborn & Wells
The Deere button switch shown in the picture is Normally Closed. Most push button switches (door bell etc.) that you have probably seen are Normally Open.

Normally Open means that the switch is "open" or doesn't complete the circuit until it is pushed in.

Normally Closed means that the switch is "closed" and completes the circuit until the button is pushed.

Think of "Normal" as meaning "If I don't touch the switch how will it behave - Complete the circuit or leave it open?"

As to whether this makes something ON or OFF depends on how the device that it is connected to behaves.

With the Deere planter switch, the button is not depressed when the planter is down in the planting position. This means that the circuit is completed until the planter is raised and the box contacts the push button switch which opens the circuit. The mechanical action of the planting unit and this switch reverses the logic in a sense.

You might ask "why don't we use a Normally Open switch and push the button when the planter is down?" Logically this would work fine but might require some complex mechanical linkage to keep the switch in the closed position as the planter units float up and down while planting.

Many whisker switches have three terminals under a cover. These terminals are usually labelled with NC, Common and NO. You use the Common terminal and usually use only one of the other terminals. Depending on whether the switch is deflected when the planter is UP or DOWN, you would use either the NC or NO terminal. The newest Ag Leader whisker switches are wired with two connectors. Basically you plug into one and if the action is backwards you plug into the other. This eliminates the confusion as you just try one or the other until it works correctly.

This means that you have the freedom to mount the whisker switch in different locations. On some planters it might be easier to have the whisker switch deflected when the planter is raised or others it might be easier to have the whisker swhitch defleted when the planter is down in planting positon. You would use either the NC or NO connection to make things work correctly.

The Deere push button switch does not have that option as it is sealed and will always behave as Normally Closed.

As long as I'm talking about switches, I'll keep going. The most common toggle switches have two terminals and are referred to as SPST which means Single Pole Single Throw. This is the common ON/OFF switch.

You may see a switch that has three terminals and is called a SPDT. This means Single Pole Double Throw. Think of this as a simple knife switch where the center terminal contacts the upper terminal when thrown one way and contact the lower terminal when thrown the other way. These switches can be used as a simple ON/OFF switch by not using one of the outer terminals but are usually used where you may want power to go to one device or another but never both at the same time.

Another switch that you may see might have four terminals and might be a DPST. This is essentially two knife switches side by side with one handle. This accomplishes the same thing as two SPST switches where the operator would flip both switches together. This allows two completely separate circuit to be controlled with a single lever or button.

Another switch that is common and has six terminals is the DPDT. This is two DPST switches side by side in a single enclosure. With the switch one way, the Left center terminal goes to its upper terminal and the right center terminal goes to its upper terminal. With the switch the other way the Left ceter terminal goes to its lower terminal and right center terminal goes to its lower terminal.

This type of switch is used in many applications. Often these switches have a center position and some are spring loaded (momentary) to return to the center position. A common use for theses switches is to wire power to one center terminal and ground to the other. The output terminals are connected in a criss-cross fashion to provide output. This arrangement is used for polarity reversing situations.

For example, with a butterfly valve in a sprayer, it is desirable to run the motor in one direction to increase the flow and the other to decrease the flow. The above switch and wiring would allow for this since a +/- polarity would be sent out with the switch in one position and a -/+ polarity would be sent out with the switch in the other position. When the switch is in the center position nothing is sent out so the butterfly stays in its current position.

Edited by tedbear 7/4/2011 06:44
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SDFarmboy
Posted 7/3/2011 23:17 (#1847480 - in reply to #1846377)
Subject: Re: Normally Open and Normally Closed


Ted:
Great explanation. Keep up the good work.
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Ron..NE ILL..10/48
Posted 7/4/2011 08:11 (#1847818 - in reply to #1847480)
Subject: Re: Normally Open and Normally Closed



Chebanse, IL

I agree...we are very lucky readers here on NAT to have Ted Thisius' informative replies. He obviously spends more than a few seconds formulating answers to share with all.

Thanks Ted!!

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Robert W Greif
Posted 7/4/2011 09:29 (#1847924 - in reply to #1846377)
Subject: Thanks Tedbear



Dallas Center IA 515-720-2463
I need to add my thanks for a good answer to my question.

You have helped me several times.

A couple weeks ago I purchased a Ag Leader Implement Switch, Wisker type.
It has two weatherhead connectors on it - One labled NO, the other NC.

Having dreams of Implement Switches on about everything, as disk ripper, disk chisel, field cultivators. Already set up on both planters and the sprayers.

And then doing 100% recorded history of field operations.
This would probably mean another Edge, and a 1500 receiver.
Plus a couple extra wiring harresses. Leave the wiring in place on a tractor. Move the box and receiver.

Back when I first got into Micro-Trak Cal-An-Acres I soon wanted the acre count on everything.
And I figured out how to get that on/off magnet on just about all the stuff.
Took me a long time to figure out how to do it on the non spray controller sprayer. Ended up one switch shut off both sprayer electric valves and Cal-An-Acre.

And I never could come up with automatic count for the 20' Brady stalk chopper.
But tillage, NH3, planting, sraying were all counted.
Never had one in the combine, but I had one of the cheaper Micro-trak yield mointors in the combine since 1992.
The one that looks like an old Cal-An-Acre and counts acres, shows speed. Counts bushels as you unload by counting unload auger revs.
Got a 'On the Go' Micro-Trak yield mointor in 1995. Put the GPS and recording stuff in 1997.

Today I still have several Cal-An-Acres, none work. Most don't work because I have not maintanded the speed imput, ie. Magnets, Radar, Or the old Micro-Trak sound deal.
I have one of the new style Cal-An-Acres, it was in the Deere 4630. I took it out pre planting. The second Hockey Puck had quit.
With the Edge I always have speed showing anyway.

But the Cal-An-Acre will measure distance in feet up to 10,000 feet.
More with a little thinking. A 3000 controller will go to about 65,000 feet.

Hope to come up to the Well MN area to see Tedbear some of these days.

Edited by Bobby Greif 7/4/2011 11:41




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