Banner QMT42 Series 400 mm Adjustable Field Sensors Manual de usuario descargar pdf (Pagina 2)

QMT42 Series 400 mm Adjustable Field Sensors

page 2 Banner Engineering Corporation

Adjustable Field Sensing - Theory of Operation

The receiver element of an adjustable field sensor produces two

currents: I1 and I2. The

ratio

of these two currents changes as the

received light signal moves along the length of the receiver element

(see Figure 1). The sensing cutoff distance relates directly to this

ratio, which can be adjusted using the sensor’s multi-turn

potentiometer.

The cutoff distance for model QMT42...AFV400 sensors is

adjustable from 125 to 400 millimeters (5 to 16 inches). Objects

lying beyond the cutoff distance are ignored, even if they are highly-

reflective.

However, it is possible to falsely detect a background object, if it is

positioned as shown in Figure 3, or if it moves past the face of the

sensor in a direction which is perpendicular to the sensing axis

(Figures 2 and 3). To solve this problem, rotate the sensor 90

degrees, as shown in Figure 4.

Lenses

Object

Background

Adjustable

Sensing Field

Cutoff

Distance

Receiver

Element

Minimum

Sensing

Distance

Receiver

Element

Emitter

Sensing Axis

Figure 1: Adjustable Field Sensing Concept

Figure 2: Sensing Axis

Figure 3: Object Beyond Cutoff Distance - Problem

Figure 4: Object Beyond Cutoff Distance - Solution

Cutoff Distance

Sensing Field

Sensor

(side view)

Cutoff Distance

Sensing Field

Sensor (top view)

As a general rule, the most

reliable sensing of an object

which approaches from the

side occurs when the line of

approach is parallel to the

sensing axis.

A reflective background

object in this position

or moving across the

sensor face in this axis

and direction may

cause false sensor

response.

A reflective background

object in this position or

moving across the

sensor face in this axis

will be ignored.

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