Hyde Park Hold on Loss of Echo Feature
In industrial applications, sensing the distance to a target is preformed using ultrasonic sensors in the proximity mode with analog outputs, where the sensor must get a return signal (an echo) from the target to determine its distance. When sensing the distance to some object, it is critical for the sensor to obtain relevant information. In sensing the level of media in a tank, it is easy to understand that when the surface of the liquified media is relatively smooth, the return echo is dependable and consistent over time. However, the application is far more challenging if the media is turbulent due to motor driven blender/beater bars, or piping inlets into a tank causing surface disturbances. Another example of a challenging application is web-loop control in a stamping operation, where the web-loop is “dancing” around in front of the sensor, and the web’s incident angle and position from side to side is without consistency.
In such challenging applications, the problem for the sensor is that, while it obtains return signals from the target to determine its distance to that target, it also randomly experiences a loss of return echo, and how the sensor processes this conflicting information is critical. In worst-case scenario’s, the sensor may receive a return echo from the target only 10% of the time, while the sensor experiences a loss of echo 90% of the time. Some traditional sensors, upon loss of return echo, automatically default their analog output to one extreme or the other; e.g., 0 or 10 volts/4 or 20 ma, or worse yet, may be unpredictable in what output they will provide during this period.
Hyde Park ultrasonic analog sensors have provisions for dealing specifically with this challenging situation. They give the user, by part number or by DIP switch selection, the ability to specify what they want the sensor to do with its output during loss-of-echo (LOE/LE) states. Hyde Park’s definition of LOE/LE state is anytime the sensor experiences loss of echo for more than one  second. When this the LOE/LE state occurs, the Hyde Park ultrasonic analog sensor product family has typically these choices of sensor analog outcomes.
No LOE/LE: If LOE/LE is not selected as an functional option, there is no provision for what the sensor will do upon a loss of echo condition.
LOE/LE Minimum: For LOE/LE state, the sensor will default to the minimum of the analog signal it provides. For a 0-10 volt sensor, the output would be 0 volts. For a 4-20 ma sensor, the output would be 4 ma. The sensor will continue to provide that output, ONLY until the sensor is able to obtain a valid return signal once again from the target and update its output with that current value.
LOE/LE Maximum: For LOE/LE state, the sensor will default to the maximum of the analog signal it provides. For a 0-10 volt sensor, the output would be 10 volts. For a 4-20 ma sensor, the output would be 20 ma. The sensor will continue to provide that output, ONLY until the sensor is able to obtain a valid return signal once again from the target and update its output with that current value.
LOE/LE Hold: For a LOE/LE state, the sensor will default to the last, most recent distance reading the sensor determined. For either a 0-10 volt or 4-20 ma sensor, if for example, if the last reading before it lost return echo was 7 volts or 12 ma output, it would continue to provide that output, ONLY until the sensor is able to obtain a valid return signal once again from the target and update its output with that current true value.
The choice of LOE/LE Minimum, LOE/LE Maximum, or LOE/LE Hold is based on what is best for the application. Unfortunately, there is no single choice that is best for all applications. The value of the LOE/LE Hold function is that it is the least “disruptive” output for a media or target experiencing a turbulent surface.
Specific Hyde Park ultrasonic analog sensor models which include one or more these LOE/LE features are the following:
SM6x2 (discrete) , SM6x6 (analog), SM5x2 (discrete); SM5x6 (analog) ; SM9x2 (discrete), and SM9x6 (analog) Series
Hyde Park ultrasonic analog sensor’s additionally have an averaging function, integrated into their logic. It is a “running average” of the last 12 return echoes. This averaging is done to mitigate the sensor responding to variations in the return echo measurement that may be untrue, or caused by disturbances that are momentary. An example of this may be an insect or fly passing in front of the sensor,
Excel Automation / Eagle Sensors & Controls are Authorized Distributors of the Hyde Park product line since 1995 and 2017, respectively. Contact us for technical, applications, or sales support.