In the 60s, we had an Amana that had as much chrome as a '59 Chevy that you had to start and stop to move the food around in to keep it from overheating in spots. The turntable came later.
I would like @14pppg to comment on what the purpose of PID control is for their project. Maybe the professor is wanting the student to say that PID isn't necessary.
I'd be looking at a way to simulate button presses on the keypad if it was my project.
PID can work if you have good feedback measurements from the system and good control over the system. Since the physics of the measurement system and the physics of the microwave control are uncertain, maybe it would be good to research how common microwaves do the automatic measurement before focusing on a PID in between the two.
One issue I see with using PID is that, for example, food heats up a lot quicker with microwaves than it cools down with radiation+convection+conduction, and that non-linearity can play havoc with a linear control system.
Magnetrons operate at extremely high voltages and generate strong microwave radiation, which can be hazardous. Be sure to take all necessary safety precautions, including using proper shielding and working with an appropriate high-voltage power supply with safety interlocks to prevent accidental exposure.
The following is a summary based on the provided links and references.
Controlling the output of a magnetron, which is typically found in microwave ovens or radar systems, involves managing the power supply and, in some cases, using additional modulation techniques. Be sure to check the magnetron's data sheet first. Hereâs a step-by-step breakdown of how to control a magnetron's output:
1. Power Supply Control
Voltage Control: The primary method of controlling the output power of a magnetron is by adjusting the voltage applied to it. Magnetrons are high-power devices that require a high-voltage power supply, typically in the range of several kilovolts.
Increase Voltage: Raising the high-voltage DC supply to the magnetron increases the output power.
Decrease Voltage: Lowering the high-voltage supply decreases the output power.
The relationship between voltage and power is approximately linear, so adjusting the power supply voltage allows for rough control over the output power.
2. Pulse Width Modulation (PWM)
Pulse Mode Operation: Many magnetrons, especially in radar applications, are operated in pulsed mode. In this mode, the magnetron is turned on and off rapidly, controlling the average power output over time.
Longer Pulse Widths: If the pulse duration is increased, more energy is delivered, resulting in higher average power.
Shorter Pulse Widths: If the pulse width is shortened, less energy is delivered, lowering the average power.
PWM is a common method of controlling magnetron output when the supply voltage cannot be easily adjusted.
3. Duty Cycle Control
In pulsed systems, the duty cycle (the ratio of the on-time to the total cycle time) can be adjusted. A higher duty cycle increases the magnetron's average power output.
For example, a 50% duty cycle means the magnetron is on half the time, delivering 50% of the maximum possible power.
4. Current Control
The output power of a magnetron is also related to the current flowing through it.
Increase Current: Increasing the current through the magnetron increases the electron flow, leading to higher microwave power output.
Decrease Current: Reducing the current will decrease the output power.
Some power supplies allow for current regulation as an indirect way to control the magnetronâs output.
5. Cathode Heating Control
The magnetronâs electron emission depends on the temperature of the cathode. By controlling the filament (cathode) heater current, you can indirectly affect the magnetronâs output.
Increase Filament Current: This increases the electron emission and boosts output power.
Decrease Filament Current: This reduces electron emission, lowering the output power.
6. Magnetic Field Adjustment (Advanced)
The strength of the magnetic field around the magnetron can influence its operation. Changing the magnetic field can affect the frequency and efficiency of microwave generation, but this is an advanced method and usually not used for basic power control.
In some cases, electromagnets are used instead of permanent magnets to allow for fine control over the magnetic field, providing a way to tune the output.
7. External Modulation Techniques
In some systems, the magnetron output is modulated using external methods, such as phase or frequency modulation. However, this is more common in communication or radar applications, not power regulation.
8. Control via Feedback Loops
In some high-precision applications, the magnetron's output power is controlled using feedback loops that monitor the actual microwave output and adjust the voltage, current, or duty cycle to maintain the desired power level.
9. Cooling System
Proper cooling is essential for stable magnetron operation. Ensuring the cooling system (either air or liquid-based) is working effectively can prevent overheating, which can impact power control and stability.