Ultrasonic Sensor Technology
Madison's ultrasonic level sensors rely on high-frequency sound waves above the range of human hearing (over 20,000 hertz) to measure level. Our ultrasonic sensors use ultrasonic sound waves to sense the level of liquids, solids or powders in airbased containers, tanks and vessels of all sizes and shapes.
Madison's sensors can be bench- or field-calibrated through communications with a PC or a push button on the sensor. This capability enables the user to define the span in the vessel and only trigger on objects within that window. Each standard model has its defined operating distance listed on the catalog chart page. Custom models can be designed for specific application needs based on the variables that can be found on the Madison Specification Work Sheet.
These ultrasonic sensors are not susceptible to error due to the target material's color, shape or composition (e.g., transparent or opaque, liquid or solid). They are particularly good for applications that must sense a non-metallic object in an environment where there is systematic, heavy wash down, liquid, dust, heavy spray, food, ink, or other environmental hazards. Since sound energy is used for detection, the reflecting object does not have to be metal, but can also be glass, plastic or even paper.
Stagnant, non-agitated liquids and solids consisting of large and hard particles are good reflectors and, therefore, good candidates for ultrasonic level measurement. Fluff, foam and loose dirt are poor reflectors, and dust, mist or humidity in the vapor space tend to absorb ultrasonic pulse. When these conditions are present, they are generally not measurable. As a rule of thumb, use 20% of the stated range of a Standard model to see if it will overcome these conditions. Where these characteristics are present, a Madison radar sensor might be appropriate.
Architecture of an Ultrasonic Level Sensing Device:
Operation Principle of Ultrasonic Level Devices:
An ultrasonic transducer matched to air is stimulated by a pulse transmitter, and it generates a pressure wave that propagates to a target and then reflects (in similar fashion to a loudspeaker). The reflected wave is received by the same transducer, in the receiver mode, and is converted into an electrical signal (as a microphone would). The electrical signal is amplified and processed to find the reflected echo and then calculated to find the distance to a specific target. Distances to a target are converted linearly to a 4-20 mA current and, optionally, information about level measurement is sent via RS232 or RS485 to a PC for processing such functions as diagnostics, programmble set-up and data logging.
Ultrasonic Sensor Still-Pipe Mounting Considerations:
No end cut is required for pipes shorter than 6".
The ID of the pipe must be greater than the OD of the transducer nozzle. If pipe is longer than 6", a 45° cut is required.
Radar Sensor Technology
If a Madison ultrasonic sensor can't measure the level of your liquid, our radar sensors can. Madison's radar sensors can detect the liquid level under a layer of airy foam and even can measure Oil/Water interfaces.
Internal piping, deposits on the antenna, multiple reflections or reflections from the wall can all interfere with the proper operation of the radar sensor. Madison's radar sensors use improved microwave pulse technology to track any target material from the tip of its antenna to the bottom of the tank. Their power, pulse widths and sensitivity depend on the distance of the target from the antenna and the dielectric constant of the reflecting material.
Madison's radar sensors feature "echo marker" signal processing, making them among the most technologically advanced pulse radar systems on the market.
This technology will provide a reliable continuous pulse shape unaffected by environmental conditions such as:
The high-resistance PTFE (Teflon®) antenna can help provide resistance to material buildup.
Simple mounting and push-button calibration make for a very easy installation. Calibration can be completed on the bench or in the field by following simple instructions. The sensor can be threaded directly into a 2" NPT metal or plastic flange. Unique application requirements can be described on the Madison Specification Work Sheet, which our engineering department will use to produce a design that meets your needs.
Architecture of a Radar Level Sensing Device:
Operation Principle of Microwave Level Devices:
The microwave rod antenna is stimulated by an electromagnetic pulse transmitter and sends very short pulses to a target. The pulses reflect from the target and then they are received back by the same antenna. The electrical signal from the antenna is amplified and processed. The distance to an object is calculated and then converted to 4-20 mA. Optionally, level information is also sent to a PC via RS232 or RS485 for diagnostic data logging and programmable set-up.
Turning the low dielectric materials operation mode ON or OFF
The ON mode is recommended for materials with a dielectric constant lower than 4 and to eliminate multiple reflections in tanks.
- To turn the low dielectric materials mode ON, push the calibration button and hold until the LED light flashes yellow, then red, and then turns off. Release the button. The blinking green LED light indicates that the low dielectric materials mode is ON.
- To turn the low dielectric materials mode OFF, push the calibration button and hold until the LED light flashes yellow, then red, then turns off. Release the button. The constant green LED light indicates that the low dielectric materials mode is OFF.
The low dielectric materials operation can also be turned ON or OFF with Madison's software during PC communications, which is recommended.
Radar Sensor Still-Pipe Mounting Considerations:
No end cut is required for the following:
|4.0" and 5.0"
End cut of 45° is required for pipes longer than 10.5"; the ID of the pipe must be greater than 6".
FCC Information for Users
Sensors have been tested and found to comply with the limits for Class A digital device, pursuant to Part 15 of the FCC rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operating in a commercial environment. These sensors generate, use, and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause interference with radio communications. Operation of this equipment in a residential area is likely to cause interference that the user will be required to correct.
Madison Company's radar sensors are highly accurate, noiseless and self-adjusting pulse radar transmitters for distances up to 100'. The sensors adjust their microwave pulse amplitude and width to a target distance and target reflection properties. The receivers change their sensitivity with the amplitude of received echoes. In addition, the sensors analyze the shapes of the received echoes and eliminate the ones coming from tank walls, standpipes and other obstructions. These features allow the sensors to track any wanted target from the tips of their rod antennas to the bottom of the tank, regardless of the tank shape or environmental conditions. For very low dielectric constant materials (≈ 2), the radar sensor needs at least 2' from the antenna tip to detect the material. Any buildup on the rod antennas does not deteriorate the performance of the radar sensors. The radar transmitters do not have any mismatch between resonator and transceiver. This eliminates problems when a target is close to the antenna and gives optimal performance of the radar sensor's very high efficiency. The Madison radar sensors also feature a low dielectric mode. In this mode, the Madison sensors will ignore echoes from tank bottoms with material present, and they will increase their transmit energy and the sensitivity of their receivers until they detect echoes from the surfaces of the low dielectric materials. This mode will work with dielectrics around 2 and higher.
Non-Contact Mounting & Installation Guidelines
Mounting of Non-Contact Level Sensors
The sensor must be installed on the top of the vessel and must be positioned to ensure that the sensor face has an unobstructed line of sight to the "empty" level of the tank. (Ultrasonic Sensors will not operate in a vacuum.)
To calculate the minimum distance from the wall for sensor placement, use:
Minimum Distance From Wall = Tangent (Beam Angle/2) (Tank Height)
The best echo is obtained when the sensor diaphragm is parallel to the surface of the material being monitored. Make sure that the material does not encroach into the dead zone (ultrasonic sensor).
In tanks with dome tops, the sensor should not be installed in the center. Place it 2/3 of the way between the wall and the center line.
Do not attempt to measure through the filling curtain. Make sure that the material or product does not encroach into the dead zone.
Avoid interference from the side of the tank or from obstructions inside the vessel. Do not install the sensor at an angle.
In tanks with domed tops, aim the sensor to point toward the discharge hole.
Installation of Non-Contact Level Sensors
Mounting the sensor correctly is critical to its proper operation. Refer to instruction manual for wiring information.
The ultrasonic sensor can be mounted directly by threading it into a 2" NPT plastic or metal mounting flange with the sensor face below the flange and pointing down, without making contact with any surface.
The radar sensor can be mounted directly by threading it into a 2" NPT metal mounting flange with the antenna pointing down. The radar sensor must be installed in a metal flange. If a still-pipe is required, it must be metal as well.
Metal Standpipe Mounting
Both ultrasonic and radar sensors can be installed utilizing a metal still-pipe. Plastic may also be used for ultrasonic.
|Pipe Diameter (Radar models*)
|4.0" and 5.0"
If your mounting material or configuration does not comply with these notes, please consult Madison Company for proper interface.
* For metal still-pipes that have a small ID and that are longer than 4" in this table, use 6" or 8" antenna extensions that are equal to or longer than the still-pipe.
Operation of Non-Contact Level Sensors
A pulse is emitted from the non-contact level sensor's transmitter. The pulse travels to the surface being monitored and is reflected off the surface, back to the sensor. The time of flight is divided by 2 and converted to an output signal directly proportional to the material level. In the case of the ultrasonic sensor, temperature is measured to compensate for the speed variation of the ultrasonic pulse
Calibration of Non-Contact Level Sensors
A single push button is used to set the "Near" (Full) and "Far" (Empty) distances for both ultrasonic and radar sensors. Calibration can be done in the vessel only if the level in the vessel can be varied for both the high and low level, each to be set independently. The sensor can also be calibrated on the bench by aiming the sensor at an appropriate target set at the corresponding distances to the "Empty" and "Full" levels. The target for Ultrasonic Sensors may be water, cardboard, wood or most any flat surfaces, while Radar Sensors require Liquids or a flat Metal surface, including a foil covered surface to properly reflect their signal. Additionaly, sensors can be set by using software programming when connected to a PC (optional hardware required). Factory-calibrated sensors can be provided; consult factory for details and pricing. The 4mA and 20mA set points are independent of each other, fully adjustable over the sensor's range and stored in a non-volatile memory. Calibration feedback is acknowledged via an LED light that turns green, yellow, or red depending on calibration procedures. For radar and long-range ultrasonic applications, it is best to calibrate the far target first and then the near target. Please review the programmable calibration procedure.
Note: Factory-supplied installation manuals are packaged with each sensor, and are also available on the appropriate product documentation tab.
Figure A.Figure B.
A. Far Target Calibration
Setting far target (empty tank) to 4 mA or 20 mA
- Begin calibration mode with the sensor LED color green. Place end of the sensor at the proper distance equal to the far target distance.
- Push button, and hold until LED turns red to set 4 mA [approx. 5 seconds.], or hold until LED turns yellow to set 20 mA [approx. 2 seconds].
- Release button, observe, LED flashes to acknowledge that the "far" target has been set.
B. Near Target Calibration
Set near target (full tank) to 20 mA or 4 mA
- Continue calibration mode with the sensors LED color green. Place the end of the sensor at the proper distance equal to the near target distance.
- Push button, and hold until LED turns yellow to set 20 mA, or hold until LED turns red to set 4 mA.
- Release button, observe, LED flashes to acknowledge that the "near" target has been set.
Note: Both the 4mA and 20mA settings need to be set to different distances. If the Empty is calibrated to 4mA, then the Full must be calibrated to 20mA, or vice versa.
Madison's standard ultrasonic and radar sensor models can be selected with a communication option. This option is a choice of an RS-232 or an RS-485 connection. The RS-232 is for a one sensor to one PC link, and the RS-485 is for up to multiple sensors (up to 128) to one PC. Madison supplies user-friendly software for sensors purchased with this option. Once the software is loaded onto the user's PC, the user can tailor several characteristics of the sensor so that the graphs and displays of the sensor's signals can be representative of the measurements being taken in the vessel.
For any Madison ultrasonic or radar model ordered with one of the optional communication ports, the interfacing software is provided. The software operates on a basic PC that is running Microsoft Windows 95™ or higher and has a serial port. Software can also be downloaded here: Communication Software for Radar and Ultrasonic Sensors Ver. 7.1 (32.9 MB .zip)
Communication is via RS232, RS485 or MODBUS RTU protocol. This requires the user to provide the wiring from the sensor terminal block under the cover to the computer. Models with RS485 communications protocol will need an RS485 to RS232 converter. The computer must have a 9-pin Serial connector or the user will need to use a Serial to USB adapter cable/connector.
NOTE: Customer MUST select either RS232 or RS485 when ordering. Typical non contact part number will be R3-50CXXX – where the "XXX" is the 232 or 485 designator. The MODBUS RTU protocol can be accessed from either RS232 or RS485.