Reference Manual

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PMAC 2 Software Reference

104 PMAC I-Variable Specifiation

For systems with PMAC2 digital current loop closure, the commutation/feedback polarity

match is independent of the servo/feedback polarity. Once Ix72 has been set for proper

commutation/feedback polarity, the proper position-loop servo/feedback polarity must still

be established.

See Also

I-variables Ix70, Ix71

Encoder I-Variable 0

Setting Up PMAC Commutation

Getting Started Section, Setting Up A PMAC-Commutated Motor

Ix73 Motor x Phase Finding Output Value

Range

-32,768 .. 32,767

Units

Bits of 16-bit DAC

Default

Remarks

WARNING:

An unreliable phasing search method can lead to a runaway

condition. Test your phasing search method carefully to make sure

it works properly under all conceivable conditions. Make sure your

Ix11 fatal following error limit is active and as tight as possible so

the motor will be killed quickly in the event of a serious phasing

search error.

Ix73 defines the magnitude of the open-loop output to be used if a power-on phasing

search is done for a PMAC-commutated motor (Ix01=1). A phasing search is required for

a synchronous motor (Ix78=0) such as a permanent-magnet brushless motor with no

absolute position sensor (Ix81=0). The phasing search is done automatically as part of the

power-on phasing search if Ix80 is 1 or 3; if Ix80 is 0 or 2, the on-line $ command must be

used must be used to initiate the phasing search.

If Ix80 is 0 or 1, the two-guess phasing search is used, and Ix73 controls the “vector”

magnitude of the open-loop output that is distributed among the phases according to the

guessed phasing angle.

If Ix80 is 2 or 3, the stepper-motor phasing search is used, and Ix73 controls the magnitude

of current forced into individual phase(s) to lock the motor to a position like a stepper

motor. In this method, if the PMAC2 is not performing current loop closure for the motor

(Ix82 = 0) and Ix72 > 128, then Ix73 should be set to a negative number of the desired

magnitude. In all other cases it should be set to a positive number. If the sign of Ix73 is

wrong for your setup, the motor will run away when the loop is closed.

Values of 2000 to 6000 are typically used for Ix73 in either method.