Near Intersection of I-35 & I-90 Southern Mn. | 77 Farmer - 3/9/2009 23:17
"The GreenStar™ 2 Rate Controller is not compatible with PWM flow control valves. THE GS2 RC can only control on/off (bang-bang) valves. "
This surely can not be the case or how would the GS2 vary the rate. The fast valve is still a proportional valve just happens to shut off also.
Also if you need the 1 1/4 valve and Raven dont offer it just put the Raven Fast Valve motor on the KZ valve body.
I am familiar with PWM valves and the concept. I have not seen PWM valves used with NH3 but apparently it is being done.
I don't know if GS2 can work with PWM, but I would think so. Especially since the Rate Controller works with planter hyd drives.
Raven and Ag Leader can and this is often done with hydraulic control valves for strip-till and other rigs where the metering device is run with an orbit motor.
Looking at control valves from a Raven point of view - there are three types: Standard - has been around for years, this is type where an electric motor is connected to a butterfly or ball valve. These are two wire and the system sends a +/- polarity of current down the wires to move the valve one way and a -/+ polarity of current to move the valve the other way. These valves are for control only and are not meant for an ON/OFF function. The majority of the time these motors are not receiving any power, they only receive power when they are asked to open or close slightly. They do not move when the system is shut down for turning around.
Next there is the Fast Close valve. These are similiar in appearance to the standard valves but the electric motor is not geared down. This valve is used for control and ON/OFF operation. The motor needs to close the valve quickly when the system is supposed to be OFF. That is why the motor is not geared down. This means that when the valve is used for control and the valve is partially open, the system must give extremely short shots of electricity to move the ball very slightly. This often results in overreaction. The standard valve is less prone to this problem since its motor is geared down significantly. The Fast Close valves often have four wires. A pair for motor power and ground and another pair to pick up the control information.
Next there is the PWM control valve. In the hydraulic situation this concept is often used and works well. Think of the PWM valve like this - there is a plunger in the valve that controls the amount of oil leaving the valve which in turn runs an orbit motor. If there is a full 12V to the coil on this plunger, the valve will open fully and the maximum flow will be delivered. On the other hand, if the voltage to the coil is 0 volts, the plunger will be closed and no oil is deliverd (OFF). If a voltage somewhere between 0 and 12V is applied, the flow will be somewhere between none and the maximum capacity.
This is where the PWM (Pulse Width Modulation) concept comes in. The circuitry inside the controller sends "shots" of electicity to the coil. The width of these "shots" determines the average positon that the plunger opens. So for a very brief period the coil gets 12V, then a period of 0 volts, then a period of 12V etc. Since these shots are going ON/OFF very rapidly the plunger can't move up and down from fully open to fully closed and hovers somewhere in between. If the width of the 12V pulse versus the width of 0 voltage is increased, the plunger will hover with a larger opening allowing more flow. The controller controls this width constantly. There is no polarity reversing, it is the width of the 12V pulse (if any) that determines the output.
PWM valves are usually two wire types since the only electricity involved goes to the coil. Some systems may actually only use one wire as the chassis ground is used for the other.
This can result in very quick and precise response which is why they are often used for hyd control.
Since the operating characteristics of the three type of valves that I mention is very different, it is important to have a controller that is compatible and also setup properly. Different controllers handle this setup procedure differently. With the 440 type Raven controllers, these are the questions that must be answered when a console is first programmed from scratch. Other controllers (Insight with Direct Command) may have a menu item where the type of control is selected.
Edited by tedbear 3/10/2009 08:40
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JD GS2 RATE CONTROLLER NH3 W/KZ CONTROL VALVE
