User`s guide

SECTION 8.0

PFE-1A AUTOMATIC OPTION

8.1 PHYSICAL CHARACTERISTICS

The PFE-1A CCD photometer allows for automatic selection of filters using the 6-position

filter sliders. A small 4-phase stepper motor is located below the flip mirror of the camera

head and provides the torque and positioning accuracy needed to exactly center the desired

filter. A bevel gear arrangement connects the stepper to the filter slider.

The 12 VDC power requirement of the stepper motor is supplied through a 9-pin circular

Amp connector, as are the four stepper control lines. The important physical and electrical

specifications for the motor used in the PFE-1A is listed in Table 8-1.

Number of Phases 4

Step Angle (full step) 7.5 degrees

Steps per Revolution 48

Holding Torque 2.8 oz.-in.

Operating Temp. Range -15 to +50° C

DC Operating Voltage 12 volts

Resistance per Winding

70W

Table 8-1. Specifications for Model PF35T-48C Stepper Motor from Nippon.

8.2 DETERMINING FILTER POSITION

Each filter position is separated by 33 full steps of the stepper motor. In order to determine

position, 165 or more full steps in either direction are delivered by the stepper motor to home

the slider against one side of its mounting. After this homing procedure, the computer or

controller determines position by keeping track of the number of 33 step intervals from the

home position. Stalling the motor against its mounting will not harm the motor or mounting

covers in any way.

The pulse rate to the stepper can be varied under computer control and the optimum rate

(fastest position change without losing steps due to slider inertia), with or without

acceleration, must be determined experimentally. For a first approximation, try a steady pulse

rate of 100 steps per second and observe whether the positions are kept accurately when

changed repeatedly.