Rockwell Automation 873C Ultrasonic Sensors - Manual (Page 2)

Background Suppression and Non-Target Objects
The analog model offers a background suppression feature
which allows the sensor to ignore all objects beyond a
specified distance. This distance is set by the user at
installation by turning the potentiometer on the end of the
sensor.
Non-target objects in the sensing field can be “hidden” from
the sensor by covering them with sound-absorbent material or
by positioning them so that their echoes are reflected away
from the sensor.
Target Considerations
Because ultrasonic sensors depend on a reflected sound
wave for proper operation, the shape, material, temperature
and positioning of the target are important. These must be
selected to return the strongest echo, otherwise the sensing
distance will be reduced or the target will not be detected.
The ideal target shape is a smooth, flat surface. Rounded or
uneven objects can also be detected, but the sensing
distances and/or analog output voltages may be reduced.
An object must be close to the sensor barrel axis to be
detected because the 873C emits ultrasonic pulses in an 8
_
cone. Targets must be within this cone to reflect the pulses
and activate the switch. The object’s surface must also face
directly toward the sensor to give a proper echo.
Material thinner than 0.01mm (0.0004in) and soft materials
such as fabric or foam rubber are difficult to detect by
ultrasonic technology because they are not adequately
sound-reflective.
Target temperatures must be at or below 100
°
C (212
°
F) for
reliable sensing. Targets at higher temperatures create
convection currents in the air near their surfaces, which
disturbs the reflection of the ultrasonic pulse.
Mounting Considerations
The control must be securely mounted on a firm, stable
surface or support. A mounting configuration which is unstable
or subject to excessive vibration may cause intermittent
operation.
An 873C sensor can be mounted with its sensing face flush to
surrounding surfaces. This does not effect sensing distance.
A mounting location should be chosen such that the target’s
surface faces directly toward the sensor.
When more than one 873C is in use, the following inter-sensor
spacings must be maintained:
6m
3m
2m
2m
2m
1.5m
Environmental Factors
The output of these devices drifts approximately 0.2% per
degree Celsius of temperature change. The analog model
output voltage drops slightly as the temperature increases,
even if the target has not moved. The sensing distance of the
discrete switching model rises with increased temperature.
Strong air turbulence and convection currents can interfere
with operation of the sensor. Installation of baffles around the
sound cone can help to reduce these effects.
Liquid splashes or heavy condensation on the face of the
sensor can interfere with proper operation. In liquid
applications, the device could be protected by relaying the
ultrasonic pulse to the surface of the liquid via a flat “bounce
panel.” Installing shielding around the sensor can also help to
reduce splash and condensation interference.
873C ultrasonic sensors are not effected by humidity, dust,
mist, or changes in atmospheric pressure.
Wiring
All external wiring should conform to the National Electric
Code and applicable local codes. Connect the proximity
switch to the power supply and load as shown in the wiring
diagrams and as described below.
1. Connect the BROWN wire from the proximity control to the
positive (+) side of the 18–30V DC supply.
2. Connect the BLUE wire from the proximity control to the
negative (–) side of the 18–30V DC supply.
3. Connect the BLACK wire from the proximity control to the
positive input of the load.
NOTE: If the positive (+) and negative (–) wires are reversed,
the switch will not operate properly. The sensor will not be
damaged because it is equipped with reverse polarity
protection.
NOTE: These switches are equipped with protection against
transient noise. However, it is recommended that the proximity
cable not be placed in the same conduit as AC power wiring.
Normally Open Switching
+ –
Load
Brn
– +
Blk
Blue
18–30V DC
PNP (Sourcing)
Analog
+ –
Load
Brn
– +
Blk
Blue
18–30V DC
PNP (Sourcing)
Wiring Switches in Series and Parallel
Series and parallel connection of this product is not
recommended.