Delta Tau GEO BRICK LV User Manual

Setting Up Feedback and Master Position Sensors 

49 

Turbo PMAC systems can interface to a wide variety of position sensors for both feedback and master 
use, either on the main control boards or through a variety of accessory boards.  This section summarizes 
the basic hardware and software setup issues; more details can be found in the appropriate hardware 
reference manuals and the Turbo PMAC Software Reference Manual. 

Note that the initial setup for feedback or master sensors is independent of any motor or coordinate 
system.  A motor or coordinate system may use the numerical value resulting from the initial hardware 
and/or software processing of a position signal, but this is not required.  It is also possible for user 
programs or commands to access these position values directly, without a motor or coordinate-system 
automatic function using them at all. 

Digital quadrature encoders are the most common position sensors used with Turbo PMACs.  Interface 
circuitry for these encoders comes standard on board-level Turbo PMAC controllers, UMAC axis-
interface boards, and QMAC control boxes. 

Quadrature encoders provide two digital signals that are a function of the position of the encoder, each 
nominally with 50% duty cycle, and nominally one-quarter cycle apart.  This format provides four distinct 
states per cycle of the signal, or per line of the encoder.  The phase difference of the two signals permits 
the decoding electronics to discern the direction of travel, which would not be possible with a single 
signal. 

 

Typically, these signals are at 5V TTL/CMOS levels, whether single-ended or differential.  The input 
circuits are powered by the main 5V supply for the controller, but they can accept up to +/-12V between 
the signals of each differential pair, and +/-12V between a signal and the GND voltage reference. 

Differential encoder signals can enhance noise immunity by providing common-mode noise rejection.  
Modern design standards virtually mandate their use for industrial systems, especially in the presence of 
PWM power amplifiers, which generate a great deal of electromagnetic interference. 

This section describes Turbo PMAC encoder hardware interface in general terms.  Consult the Hardware 
Reference Manual for your particular configuration for details. 

Turbo PMAC’s encoder interface circuitry employs differential line receivers, but is configured at the 
factory to accept either single-ended or differential encoders.  In this configuration, the main (+) line is 
pulled up to 5V, and the complementary (-) line is tied to 2.5V with a voltage divider.  With a single-
ended encoder, the single signal line for each channel is then compared to this reference voltage as it 
changes between 0 and 5V.