Ultrasonic Technology
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1. How does ultrasonic work?
An ultrasonic sound pulse is emitted up to 3 times per second from the base of the transducer. The pulse travels through air, reflects against the process medium below and returns to the transducer. The sensor measures the pulse time of flight between sound generation and receipt, and translated this into distance or liquid level height within the vessel. Click to view ultrasonic white paper.
2. What are the advantages of ultrasonic?
Application media often has challenging characteristics that can negatively impact level sensor performance and/or installed life. Factors include corrosive, ultrapure, coating, scaling, dirty, Δ density, dielectric or conductivity that are poorly suited for contact measurement. Ultrasonic technology is inherently non-contact, and therefore impervious to the above application factors. Click to view ultrasonic white paper.
3. What should I avoid with ultrasonic?
The factors to avoid with ultrasonic are extreme foam, vapor, turbulence and installations in flange fittings with tall risers. Foam, vapor and turbulence can absorb and/or deflect away a substantial portion of the return signal. Tall installation fittings can disrupt the acoustic signal path. Appropriate product selection and installation may be critical to overcoming such factors. Click to view ultrasonic white paper.
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Sensor Selection
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1. What are NPT and G mounting threads and where are they used?
NPT (National Pipe Threads) are the American standard tapered threads applied throughout North America, South America and parts of Asia. G (metric) ISO threads are the European standard straight threads applied throughout Europe and parts of Asia. G thread products come with a Viton® gasket for compression seal against the wrench flat.
2. What are the standard and custom sensor cable lengths?
The standard product cable length is 10' (3m). Custom cable lengths are offered in 25' (7.6m) or 50' (15.2m) increments via special order.
3. How do I select the best sensor range for optimum performance?
In most applications, select a sensor range that matches the tank height. In more challenging applications with substantial foam, vapor and/or turbulence, select a sensor range that is double the tank height. Click to view ultrasonic white paper.
4. What are the sensor materials of construction?
The electronic enclosures are fire retardant polycarbonate. The cables are polypropylene and the transducers are PVDF Kynar®. The gasket used only on the G thread product is Viton®. Click to view chemical compatibility chart.
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Sensor Installation
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1. How do I identify the best mounting location for the sensor?
The sensor should be located so that the acoustic signal path is free of obstructions from side-walls, ladders, pipes, mixers and other instruments. The sensor should be mounted level and/or perpendicular to the liquid surface. Click to view ultrasonic white paper. If substantial foam, vapor and/or turbulence are present, install the sensor in a stand-pipe. Click to view stand pipe installation tech-tip.
2. What types of installation fittings are recommended for the sensor?
The sensor can be broadly installed in tank adapters, couplings, flanges, brackets and stand pipes of appropriate size relative to the transducer. Generally, select a fitting type that will allow the installed transducer to extend through or ideally be flush with the opening to the tank. Avoid fitting types that substantially recess the transducer into the fitting, or compress the transducer against an inner wall or pipe stop.
3. How tight should the sensor be installed within the fitting?
In most applications, the sensor is hand tightened only within the fitting. If you use a wrench or tool, be careful not to over-tighten the sensor within the fitting.
4. What's the maximum flange riser height in which the sensor can be installed?
The sensor can be elevated up to a maximum of 12" high in a 6" diameter riser, 8" high in a 4" diameter riser, 6" high in a 3" diameter riser and 3" high in a 2" diameter riser. Click to view ultrasonic white paper.
5. What's the best pipe ID size for use in stand-pipe installations?
Sensors with a 1" transducer should be installed in 2" stand-pipes. Sensors with a 2" transducer should be installed in 3" stand-pipes. Click to view stand pipe installation tech-tip.
6. What's the best way to install the sensor on a sloped or dome top tank?
On a plastic tank, use a self-aligning bulk head fitting that enables the sensor to be rotated to the level and/or perpendicular position relative to the liquid surface. On a metal or fiberglass tank, a flange fitting with a riser that accommodates for the slope is typically the best option.
7. What's the best way to install the sensor with an open top tank or sump?
The LM50-1001 (2" NPT) or LM50-1061 (2" G) side mount bracket is a good choice. Add a 2" to 1" reducer bushing for use with 1" transducer sensors. Users often fabricate equivalent brackets based on their custom size or material requirements.
8. Can I install two sensors in a single tank or sump?
If the tank has an enclosed top, to avoid signal cross talk interference, only one sensor may be installed unless the second sensor is mounted in a stand-pipe. If the tank has an open top, then two sensors can typically be applied assuming that they are installed on opposing sides of the tank with at least 10' (3m) distance between one another.
9. Can the sensor be submersed in liquid?
NEMA 6 enclosure sensors are designed to resist infrequent submersion for short periods of time. NEMA 4 enclosures are designed to resist frequent splashing the equivalent of direct hose spray and should never be submerged.
10. What is the maximum 4-20 mA signal distance?
The sensor can be installed up to 1000 feet away from its point of termination using a shielded, 18-20 gauge twisted pair cable and 24 VDC power supply. The total loop resistance should not exceed 900 ohms.
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Sensor Calibration
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1. What does 4-20 mA span represent?
The 4-20 mA represents the sensor's measurement span. The 4 mA set point is typically placed near the bottom of the empty tank, or the greatest measurement distance from the sensor. The 20 mA set point is typically placed near the top of the full tank, or the shortest measurement distance from the sensor. The sensor will proportionately generate a 4 mA signal when the tank is empty and a 20 mA signal when the tank is full.
2. What are the benefits of 4-20 mA analog signals?
The old 10-50 mA standard lost the battle to 4-20 mA due to the following benefits: 1) The same two-wires carry both the sensor power and signal, 2) 4-20 mA is easily converted to a 1-5 VDC input via a 250 Ohm, _ Watt resistor or 1-10 VDC input via a 500 Ohm, _ Watt resistor, 3) 4-20 mA is low current and therefore has a low heating loss through the signal wire, and 4) with shielded cable, 4-20 mA is noise resistant to radiated and inducted interference.
3. What is the basic 4-20 mA target calibration procedure?
The sensor can be calibrated in about a minute using a 24 VDC power supply, tape measurer and flat reflective target such as a wall or liquid in the tank. To calibrate the 4 and 20 mA set points, attach the calibration wire to the appropriate power supply leg (see manual), and hold the sensor at the desired range to the target until the blue LED blinks.
4. Do I need to target calibrate the sensor in the tank?
It's often more convenient to target calibrate the sensor against a wall or other flat reflective surface using a tape measurer for 4 mA and 20 mA set point distance.
5. Do I have to calibrate the 4-20 mA span?
While the 4 mA and 20 mA set point calibration is not fundamentally required, it's generally recommended because it optimizes the sensor's installed performance.
6. Can I reverse the span from 4-20 mA to 20-4 mA?
The sensor can be reverse calibrated such that the 20 mA set point is empty and the 4 mA set point is full. Reverse 20-4 mA calibration can also help optimize the sensor's response time in applications with a fast rate of level change.
7. How do I calibrate the sensor for optimum performance installed in a flange with riser?
The 20 mA tank full set point should be placed at a distance that's greater than or equal to the riser height plus half the sensor's dead band. For example, based on an LU13 sensor, if the riser height is 6", and the dead band is 4", then the 20 mA full set point would be placed at 8".
8. Can I calibrate the 4-20 mA span without viewing the blue LED?
The 4-20 mA span can be calibrated by measuring the current consumption alone with a digital multi-meter or display. During the initial moments of calibration, the sensor draws 22 mA while it's acquiring the target distance. At the time that the sensor places the set point, the current will jump down to the appropriate 20 mA or 4 mA set point and the blue LED will flash.
9. Can I place a loop powered indicator in series with the 4-20 mA loop?
Yes, as long as the total loop resistance is less than 900 Ohms.
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Sensor Diagnostics
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1. What should I expect of the LED and signal output during normal sensor operation?
During normal operation, the blue LED should be off and the 4-20 mA signal output should be relatively stable within the span.
2. What does it mean when the blue LED is on and the signal output is 22 mA?
If the sensor does NOT receive a valid acoustic signal return, the blue LED will turn on, and the signal output will go to 22 mA until the sensor acquires the level. This is generally caused by the presence of substantial foam, vapor and/or turbulence. Click to view ultrasonic white paper.
3. What does it mean when the blue LED is rapidly flashing and the signal output is 22 mA?
If the sensor DOES receive a valid acoustic signal return, but the level falls below the calibrated 4 mA empty set point, the blue LED will rapidly flash on and off, and the signal output will go to 22 mA until the level rises back into the span. The solution is to perform a factory reset on the sensor, re-calibrate the span and place the 4 mA empty set point lower in the tank.
4. What does factory reset do to the sensor and how is it done?
Factory reset washes out any previous user calibration and returns the sensor to the original set points. Connect the white wire to the black wire (see manual), point the sensor into open space with no reflective targets, power it up for 2 seconds, and then power it down. The blue LED will not flash during reset.
5. Who do I contact for support?
Domestic sales and technical support at us.sales@flowline.com or International sales and technical support at int.sales@flowline.com.
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