Delta Tau GEO BRICK LV User Manual

Delta Tau Data Systems has provided many safety features on the Turbo PMAC controller, and invested 
many resources to make Turbo PMAC a safe product.  However, the ultimate responsibility for the safety 
of a control system using Turbo PMAC must lie with the system designer, utilizing the safety features on 
Turbo PMAC and in other parts of the system. 

Turbo PMAC has three following error limits for each motor. Following error is the difference between 
the commanded position and the actual position at any time.  The following error limit is an important 
protection against serious system faults such as loss of feedback, which can cause dangerous conditions 
like full speed runaway. 

One of these limits (Ixx11) is a fatal limit which causes a shutdown of the motor: servo loop opened, zero 
output commanded, amplifier disabled (i.e. the motor is killed), moves for the motor and programs for the 
motor’s coordinate system aborted.   

Which motors get killed – only the offending motor, all in the coordinate system, or all in Turbo PMAC – 
is determined by bits 21 and 22 of Ixx24 for the faulted motor.  This limit is intended for conditions in 
which something has gone seriously wrong (e.g. loss of feedback or power stage) and all operation should 
cease.   

After the motor or motors have been killed due to the fatal following error limit, closed-loop control can 
be re-established with the J/ command (single motor), the A command (coordinate system), or the 
<CTRL-A> command (entire card). 

Although this limit may be disabled by setting Ixx11 to zero, but this is strongly 
discouraged in any application that has the potential to kill or injure people, or 
even to cause property damage.  Disabling the fatal limit removes an important 
protection against serious fault conditions that can cause runaway situations, 
bringing the system to full power output faster than anybody could react. 

Good tuning of the motor’s servo loop is important for safety reasons as well as performance reasons.  
The smaller the true following errors are made during proper operation, the tighter the Ixx11 limits can be 
set without getting nuisance trips.  Particularly important in this regard are the feedforward terms that can 
dramatically reduce the errors at high speeds and accelerations. 

The second limit (Ixx12) is a warning limit – when exceeded, Turbo PMAC sets status bits for the motor 
and the motor’s coordinate system, and can set output lines on the control panel connector, the machine 
connectors, and through the programmable interrupt controller (for ISA and PCI bus Turbo PMACs).  
This permits special action to be taken, either by Turbo PMAC itself through a PLC program, by the host, 
which can find out through an interrupt or by polling the card, or by an operator notified with one of the 
external signals. 

The warning following error status bit for the motor can be used as the trigger condition for any of Turbo 
PMAC’s automatic triggered moves (homing-search move, jog-until-trigger, programmed RAPID-mode 
move-until-trigger) if bit 0 of Ixx97 is set to 1.  This permits easy implementation of tasks such as homing 
into a hard stop, torque-limited screwdriving, etc.