Maximum allowable frequency for encoder inputs on Master

Question

What is the maximum allowable frequency for the encoder inputs on a Master?

Answer

With Master 800, 2400, and 2410, as well as early revisions of Master 810, the maximum data rate for encoder input is 300 kHz.

On a standalone sensor, with the encoder directly wired into the I/O port or through a Master 100, the maximum encoder rate is about 1 MHz.

With revisions of Master 810 that provide setting DIP switches, the maximum frequency is 6.5 MHz.

If you are using Master 810 with an encoder that runs at a quadrature frequency higher than 300 kHz, you must use the device's divider DIP switches to limit the incoming frequency to 300 kHz.

The DIP switches are located on the rear of the device.

This section describes how to set the DIP switches on Master 810 to do the following:

• Set the divider so that the quadrature frequency of the connected encoder is compatible with the Master.
• Set the debounce period to accommodate faster encoders.

Setting the Divider

To set the divider, you use switches 1 to 3. To determine which divider to use, use the following formula:

Output Quadrature Frequency = Input Quadrature Frequency / Divider

In the formula, use the quadrature frequency of the encoder (for more information, see Encoder Quadrature Frequency) and a divider from the following table so that the Output Quadrature Frequency is no more than 300 kHz.

The divider works on debounced encoder signals. For more information, see Setting the Debounce Period.

Encoder Quadrature Frequency

Encoder quadrature frequency is defined as illustrated in the following diagram. It is the frequency of encoder ticks. This may also be referred as the native encoder rate.

You must use a quadrature frequency when determining which divider to use (see Setting the Divider). Consult the datasheet of the encoder you are using to determine its quadrature frequency.

Some encoders may be specified in terms of encoder signal frequency (or period). In this case, convert the signal frequency to quadrature frequency by multiplying the signal frequency by 4.

Setting the Debounce Period

If the quadrature frequency of the encoder you are using is greater than 3 MHz, you must set the debounce period to “short.” Otherwise, set the debounce period to “long.”

You use switch 4 to set the debounce period.