RPS-4000 Ultrasonic Level Sensor
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self-contained Ultrasonic Level Sensors provide
level control of both liquid and bulk materials.
This gives the user a viable alternative to
bubblers, floats, capacitance probes, and pressure
ranges of 30 and 40 feet respectively many tanks
are within reach. The incorporation of a
microprocessor design makes it possible to achieve
signal conditioning. This gives the ultrasonic
sensor the ability to process the return
ultrasonic echo and distinguish between false
targets and real targets.
incorporation of a microprocessor into the design
of the RPS-3000PVC and RPS-4000 ultrasonic level
sensors, many of the common problems facing long
range sensing applications have been overcome.
Software was then written to optimize the
performance characteristics of the sensors. The
artificial intelligence analyzes and conditions
the return ultrasonic echo. This process filters
out any false echoes and electrical noise. An
additional task that the microprocessor does is
is a brief list of features for the RPS-3000PVC
SIMPLE CALIBRATION: The sensing window can
be adjusted by using one of three easy methods.
NOTE: When the sensors are powered up and the
control lines not used, they are factory preset to
NON-CONTACT: The use of ultrasonic sound to
measure distance means that the sensor does not
need to come in contact with the target.
TEMPERATURE COMPENSATED: This is
accomplished by means of a temperature probe that
is built into the transducer head.
ANALOG OUTPUT: These sensors provide a
4-20mA analog output that is proportional to the
changing distance. This output can be inverted.
SENSITIVITY CONTROL: This enables the gain
of the sensor to be adjusted to work best in
different tanks and on different materials.
EASY INSTALLATION: Both of these sensors
are contained in a standard 30mm housing. They
come with two jam-nuts for simple mounting.
SELF-CONTAINED: There are no remote boxes
to mount with these sensors. All necessary
electronics are contained within the sensor.
LED INDICATOR: This indicates the detect
state of the sensor as well as the strength of the
return echo. This feature helps to insure proper
alignment during installation.
AFFORDABILITY: These sensors were designed
to be cost competitive and to solve applications.
MICROPROCESSOR DESIGN: The incorporation of
a microprocessor allowed software to be written to
solve many of the common problems that needed to
be overcome with long range applications.
HOW TO CALIBRATE
(and possibly the most direct way to calibrate the
sensing range) is as follows (see figure B):
Step 1: Tie the Red/Yel wire (20mA control
line) and the Red/Blue wire (4mA control line)
Step 2: With the material level at the 4mA
point, usually the low level, connect these lines
to ground (Green wire) for one second.
Step 3: With the material level at the 20mA
point, usually the high level, connect these lines
to plus (Red wire) for one second.
The sensor is now calibrated and will generate the
analog 4-20mA output between these two points.
NOTE: When completed, the two control lines
should remain tied together. To change the window,
disconnect these two wires for one second and then
reconnect them. Then repeat steps 2 and 3. The far
point should always be programmed first, then the
Method Two calibrates the sensors by
using the following charts (see figure C):
This indicates that the control line is not tied
to anything. It is left floating.
High: The control line is tied to plus (Red
Low: The control line is tied to ground
When using these charts to calibrate the sensors
the analog output will occur over the full range
of the selected sensing window. The 20mA will be
at the near distance and the 4mA will be at the
One advantage of calibrating the sensors this way
is that there is no need to fill the tank to the
high and low limits. Another advantage is that
once the sensor is installed there is no need to
go back to it to program. This can be done at a
remote location at the end of the sensor's cable.
calibrates the sensors by using resistors tied to
the control lines (see figure D). These resistors
are installed between the control lines and ground
(green wire). The following resistance formula
applies for distance:
1Kohm = 1 foot.
For example if a range of 5' to 15' is desired
with an analog output of 20mA at 5', and 4mA at
15', the following resistor values should be
15' = 15Kohm resistor tied to 4mA control line
5' = 5Kohm resistor tied to 20mA control line
The output will now start at 5' 20mA and decrease
with distance to 15' 4mA. The output can be scaled
in the opposite direction by reversing the values:
5' = 5Kohm resistor tied to 4mA control line
15' = 15Kohm resistor tied to 20mA control line
The output now starts at 5' 4mA and increases with
distance to 15' 20mA.
Potentiometers can be used in place of fixed
resistors and then the proper distances can be
The advantage with this method, as with the second
way of calibrating, is that the tank does not need
to be filled to its high and low limits during
setup. In addition these set points can be
adjusted at a later time without going to the top
of the tank.
HOW TO USE THE GAIN CONTROL
The RPS-3000PVC and RPS-4000 sensors provide the
user with gain control. This is controlled by the
Red/White wire (see figure E). When this wire is
left open (floating) the sensors are operating at
their maximum sensitivity. The sensor's gain can
be reduced by doing the following:
Install a 100Kohm potentiometer or a fixed value
resistor across the gain control line (Red/White
wire) and ground (Green wire). With the
potentiometer set at 100Kohm, the gain or
sensitivity of the sensor is at its maximum. When
the potentiometer is set at 75Kohm, the
sensitivity is 75% of full gain. If the
potentiometer is turned all the way down which is
equivalent to shorting the gain wire to ground,
the sensor is at minimum sensitivity.
The sensitivity/gain control allows the sensor to
be adjusted to work best in different tanks and on
different materials. This control does not need to
be used. If the sensor is installed and works well
with full sensitivity there is no need to reduce
the gain. However if the sensor is installed and
it seems to be detecting something other then the
desired target, the gain can be reduced to see if
the false target disappears.
The LED is located at the back of the sensor. It
provides by way of color various indication as to
the sensor's functions. Its primary purpose is to
insure proper alignment during installation. The
following colors indicate:
Green: The sensor has power and is in the
Yellow: The sensor has detected a target but is
receiving a weak signal. It may be that the sensor
is not properly aligned to the material or that
the target is providing a weak return echo.
Red: This indicates that the sensor is detecting
the target. The brighter the shade of red the
stronger the return echo. This indicates the
sensor is properly aligned and the target is
providing a good reflective surface.
NOTE: It may not always be possible to get a
bright red signal. This is because various
materials will have different reflectivity
characteristics. However, as long as the sensor
stays in the yellow to red state, enough return
signal is being received and the sensor will
The RPS-3000PVC and RPS-4000 provide an analog
current output of 4-20mA. This output is
proportional to the changing distance that has
been programmed. The output load rating of the
sensors are 0 to 500 ohms.
QUICK DISCONNECT CONNECTOR
At the rear of the sensor, there is a water tight
quick disconnect connector. This allows the sensor
to be easily removed from the tank should this be
The RPS-3000PVC and RPS-4000 long range ultrasonic
sensors incorporate a high speed
microcontroller/microprocessor. Software was then
written to optimize the performance
characteristics of the sensors. This artifical
intelligence analyzes and conditions the return
ultrasonic echo. This process filters out any
false echos and electrical noise. An additional
task that the microcontroller does is temperature
compensation. This allows the sensor to have a
more accurate output over varying temperature
ranges. Thus with the incorporation of a
microcontroller many of the common problems facing
long range sensing applications have been
Ultrasonic Level Sensor
Adjustable 2' to 30'
Adjustable 2' to 40'
20 - 30 VDC
Reverse Polarity Protected
-20ºC to 60ºC
or -5ºF to 140ºF
0% - 95% Non-Condensing
Epoxy filled PVC
housing with PVC sensing face
RPS-4000: Epoxy filled PVC housing
with Glass Reinforced Epoxy sensing face
Current Soucing Analog Output
4 - 20mA Inverted & Non-Inverted
Short Circuit Protected
Output with 500 card:
0 - 10VDC, 4 -
with Zero, Span, Sample,
and Hold controls.
RPS-4000: 41 kHz
This equals the
sensore maximum distance
x 10mSec. For example if the maximum
programmed distance is 10' the transmit
time is 100mSec.
B-Wiring Diag. for programming method #1
C-Wiring Diag. for programming method #2
D-Wiring Diag. for programming method #3
E-Wiring Diag. for gain control
F-Connector Diagram (Male View)
"QD" cables are sold
||2' - 30'
with PVC Sensing Face
||2' - 40'
with Glass Reinforced Epoxy Sensing Face
||6' Cable with "QD"
16' Cable with "QD"