Near Intersection of I-35 & I-90 Southern Mn. | Here's a little information as to what the EMD for PWM does.
Most controllers have the ability when set correctly to work with PWM. PWM stands for Pulse Width Modulation. Pulse Width Modulation is used for many things. The way it works is that the controller sends out a 12V shot followed by a gap of zero volts. In actuality they often do this with ground instead of the hot but the idea is the same.
This pattern of ON then OFF is repeated rapidly at a certain frequency (maybe 100 times a second). So within that 1/100 of a second, the voltage could be ON all the time, OFF all the time, or ON part of the time and OFF the remaining portion. Thus the name Pulse (shot) Width (how the ON time compares to the total) Modulation (change).
A term that is used is duty cycle. This is the portion of the ON time compared to the total time. If the ON time and the OFF time are each half of the time slice, then the duty cycle would be 50%. The duty cycle can range from 0% (always OFF) to 100% (always ON).
Since this ON/OFF business happens so rapidly a plunger in a hydraulic valve can not fully open or fully close and tends to "hover" in a position somewhere between. The same is true of a 12V motor. It will run at a speed somewhere between stop and maximum. When the controller detects that the applied rate is a bit low, it will increase the ratio of the ON to OFF time (duty cycle) in an attempt to increase the applied rate to match the target rate.
Since the controller can do this why the need for EMD device? One of these is needed in high current situations such as a fertilizer pump because the controller is not wired to handle high current demands. For lower current demands such as hydraulic valves, the controller can handle them directly without the need for the EMD.
The EMD takes power/ground directly from the vehicle battery through some heavy wires. It takes its ques from the controller and Outputs that pattern through some heavy wires to the fertilizer pump. Thus the electrical load on the controller is small since it is not running the pump directly. The pump is being run through the heavy wires to and from the EMD.
For this to work, the EMD must be healthy. It must be connected to the tractor battery with heavy wires. The controller must be setup correctly to produce the PWM output since the EMD just mimics that output to the pump.
The crack in the housing would seem troubling to me. |
Micro Trak emd pwm
