The dataTakers have a single Phase Encoder counter channel, which increments or decrements counts according to the phase relationship between two pulse trains from a Phase Encoder device.

The Channel Expansion Module (CEM-AD) does not support a Phase Encoder input.

The phase encoder is an implementation of the low speed counters of the digital input channels.

The phase encoder has a variety of applications, for counting bi-phasic pulse trains from linear and rotary motion sensors. These types of sensors are collectively referred to as phase encoders.

The phase encoders output two digital pulse trains, each with the same period but with a phase difference of approximately 90°.

The two digital signals are applied to digital input channels 3 and 4 (3DS and 4DS). The phase encoder support provided by the dataTaker is implemented as counter 1PE.

The phase encoder is able to count at up to 10 Hz, and may be used

as an accumulating counter, which totalises the digital pulses forever. When the accumulating counter is read, the current contents of the counter register is returned

as a resetting counter, which totalises digital pulses during the interval between readings. When the resetting counter is read, the current contents of the counter register is returned, and the register is reset to zero

The phase encoder is a 16 bit up down counter, and counts over the range of -32768 to 0 to 32767. The counter begins from zero and counts up or down depending on the phase relationship of the input pulses.

Basic Concepts of Phase Encoding

As an example of a phase encoding device, consider a half opaque disk with two light sensors placed at 90 degrees to one another as illustrated in Figure 115.

As the disc rotates, the light paths are sequentially blocked and unblocked thereby causing the output signal from the light sensors to pulsate. The direction of movement is determined by the dataTaker from the pattern of these pulses.

Using the principle described above, but with 360 light/dark transitions on the disk, then the angle of rotation of the disk can be determined as with a precision of ±1 degree.

 

 

Figure 116 ñ A Simple Phase Encoder

Figure 116 below illustrates the output signals from the phase encoder and the value of the counter, as the wheel rotates clockwise for 2 turns, and then rotates counter-clockwise for 2 turns.

 

 

Figure 117 ñ Operation of a Phase Encoder

 

When the input to channel 3D is low, then the direction of the transition input to channel 4D determines the direction of counting. The counter is incremented on a transition from 1 to 0 and decremented on a transition from 0 to 1.

The maximum frequency of the phase encoder is determined by the sample period for the digital input channels which is defined by the setting of Parameter13 (See Section II ñ Low Speed Counters).

Connecting a Phase Encoder

A Phase Encoder can be constructed in various ways, The most common construction however is either

2 microswitches follow individual cam wheels to produce a bi-phasic pattern of contact closures

2 LED/phototransistor pairs which are chopped by a patterned opaque/translucent disc to produce a bi-phasic pattern of logic states

 

 

Figure 118 ñ Connecting a Phase Encoder

 

Reading as an Accumulating Counter

The phase encoder is operated as an accumulating counter and the data is returned when a Schedule containing the channel is executed.

Using DeTransfer, the command for example

instructs the dataTaker to read the current value for the Phase Encoder counter channel 1.

The PE specifies an accumulating Phase Encoder counter, and the data is returned in units of Counts.

The dataTaker will read the Phase Encoder counter every minute, and readings are stopped by the H (Halt) command.

DeLogger does not support the Phase Encoder input type. However the User channel type (DeLogger Version 4.2.15 or later) can be used to enter the DeTransfer commands above.

Reading as a Resetting Counter

The phase encoder is operated as a resetting counter and the data is returned when a Schedule containing the channel is executed.

Using DeTransfer, the command for example

instructs the dataTaker to read the current value for the Phase Encoder counter channel 1, and reset the counter to zero.

The PE specifies an accumulating Phase Encoder counter, and the data is returned in units of Counts. The R channel option specifies that the phase encoder is to operate as a resetting counter.

The dataTaker will read the Phase Encoder counter every minute, and readings are stopped by the H (Halt) command.

DeLogger does not support the Phase Encoder input type. However the User channel type (DeLogger Version 4.2.15 or later) can be used to enter the DeTransfer commands above.