How to Control the Speed of a Motor Using Pulse Width Modulation

Connect the terminal block to the PWM module and PLC

Connect the ACC-TB32M terminal block to the IO-SD0032PPWM PWM module using the ACC-SBC15E terminal block cable, and connect the PWM module to the Maple PLC.

Power the Maple PLC

Wire 24V from the power supply to the 24V terminal on the Maple PLC, and wire 0V from the same power supply to the 24G terminal on the PLC.

Power the terminal block

Wire 24V from the same power supply to terminal block point A10 and jumper it to B10 to distribute 24V across the terminal block. Then wire 0V to A20 and jumper it to B20.

Select the PWM output channel

In this example, PWM Frequency Group A and Channel 4 are used. That output point corresponds to terminal B4 on the terminal block.

The PWM module has Frequency Groups A, B, and C, with four channels in each group for a total of 12 channels.

Wire the PWM signal to the DC motor drive module

Connect terminal B4 from the PWM output to the positive input on the DC motor drive module. Then connect 0V from terminal A20 to the negative input on the drive module.

Power the DC motor drive module

Use another power supply to provide 24V to the DC motor drive module, and connect 0V from that same power supply to the drive module negative terminal.

A second power supply is shown in this example, but one power supply may be enough if it can deliver the required current.

Connect the drive module to the motor

Connect the DC motor drive module output to the motor by wiring the positive output to the positive motor terminal and 0V to the negative motor terminal.

Review the PWM enable logic

Open the ladder diagram section that enables the PWM module output channel instead of using the PWM Configuration GUI.

Determine the hexadecimal value for Channel 4

Use a programmer calculator together with the PWM hexadecimal chart to calculate the enable value for Channel 4. In this example, Channel 4 corresponds to bit 3, which results in hexadecimal value H0008.

The PWM module has 12 output channels, so the correct bit pattern must be converted to hexadecimal before using the TO instruction.

Enter the enable instruction in the ladder diagram

Use the instruction [TO H0001 0 H0008 1] with internal bit M00 to enable PWM output Channel 4 on the module installed in slot 1.

In this instruction, H0001 is the slot, 0 is the PWM output enable buffer, H0008 is Channel 4, and 1 is one word.

Calculate hexadecimal values for multiple channels if needed

If you want to enable more than one channel, combine the bit values in binary and convert them to hexadecimal. For example, Channels 4 and 1 equal H0009, while Channels 8, 4, and 1 equal H0089.

Enable the first speed stage

Turn on internal bit M01 to enable the first speed-control stage in rung 4.

Start the 10-second timer

Use TON TC0 100 to start a 10-second ON timer. When the timer completes, T0 turns on.

TC0 is timer bit 0, and 100 represents 10 seconds in this example.

Write the ramp time, duty cycle, and frequency

Move 500 into D10 for a 5-second duty cycle ramp time, move 25 into D20 for a 25% duty cycle, and move 500 into D30 for a frequency of 500 Hz. Then write those values to the PWM module buffer memory.

Buffer 33 is duty cycle ramp time, buffer 13 is duty cycle ratio, and buffer 1 is frequency value.

Advance to the next speed stage

When T0 turns on after 10 seconds, reset M01 and set M02 so the first stage turns off and the next logic stage begins.

Enable the second speed stage

Use internal bit M02 to enable rung 7 and begin the second speed-control stage.

Start the second 10-second timer

Use TON TC1 100 so the second speed stage runs for 10 seconds before advancing.

Write the new PWM values

Move 500 into D40 for the ramp time, 90 into D50 for the duty cycle ratio, and 500 into D60 for the frequency value, then write those values to the PWM module.

This stage increases the motor speed from 25% to 90% duty cycle at 500 Hz.

Advance to the next stage

When T1 turns on, reset M02 and set M03 to hand control to the next logic stage.

Enable the third speed stage

Use internal bit M03 to enable rung 10 and begin the third PWM stage.

Start the third 10-second timer

Use TON TC2 100 so the third speed stage runs for 10 seconds before advancing.

Write the reduced PWM values

Move 500 into D70 for the ramp time, 50 into D80 for the duty cycle ratio, and 500 into D90 for the frequency value, then write those values to the PWM module.

This stage reduces motor speed from 90% to 50% duty cycle at 500 Hz.

Advance to the final stage

When T2 turns on, reset M03 and set M04 so the final speed stage begins.

Enable the final speed stage

Use internal bit M04 to enable rung 13 and begin the final PWM speed stage.

Start the final 10-second timer

Use TON TC3 100 so the final speed stage runs for 10 seconds before shutting the motor down.

Write the final PWM values

Move 500 into D100 for the ramp time, 20 into D110 for the duty cycle ratio, and 500 into D120 for the frequency value, then write those values to the PWM module.

This stage reduces motor speed from 50% to 20% duty cycle at 500 Hz.

Turn the motor off

When T3 turns on after 10 seconds, reset M04 so the rung turns off and the motor stops.

Go online with the PLC

In MapleLogic, go to Online > Link + Download + Monitor to download the project and establish online communication with the PLC and PWM module.

Enable PWM Channel 4

Click the M00 bit and press Shift + Enter to turn M00 ON. This enables PWM Channel 4.

Start the first speed stage

Click the M01 bit and press Shift + Enter to turn M01 ON. This enables the TON TC0 100 instruction. The motor ramps from 0% to 25% duty cycle at 500 Hz over 5 seconds, and after 10 seconds T0 turns ON, resets M01, and sets M02.

Watch the motor increase from 25% to 90% duty cycle

When M02 turns ON, the second timer stage begins. The motor ramps from 25% to 90% duty cycle at 500 Hz over 5 seconds. After 10 seconds, T1 turns ON, resets M02, and sets M03.

Watch the motor decrease from 90% to 50% duty cycle

When M03 turns ON, the third timer stage begins. The motor ramps down from 90% to 50% duty cycle at 500 Hz over 5 seconds. After 10 seconds, T2 turns ON, resets M03, and sets M04.

Watch the motor decrease from 50% to 20% and stop

When M04 turns ON, the final timer stage begins. The motor ramps down from 50% to 20% duty cycle at 500 Hz over 5 seconds. After 10 seconds, T3 turns ON, resets M04, and the motor turns OFF.