How to Measure the Level of Material in a Large Bin or Hopper

Let's say you have a large bin or hopper and you regularly fill it with wood chips or powder or even liquid. How can you accurately measure the level in the bin?  In applications where it is necessary to measure the level of material in a large collection bin, there is not always an obvious way. This article will describe one method, using an ultrasonic sensor.

Purchase an industrial ultrasonic sensor (uses sound waves) with a range long enough to bounce from the top of the bin down to the lowest possible level of the material, or at least the lowest level that you care to measure. Be sure to select an ultrasonic sensor with an analog output.  Be aware that all ultrasonic sensors have a "blind zone" beginning at the face of the sensor and extending to various distances away. For this reason, the material to be measured should never be allowed to enter this "blind zone" because accurate measurement cannot take place in this range.  Also note that ultrasonic sensors are affected by drastic changes in temperature and may need to be re-calibrated occasionally.

Install the ultrasonic sensor in the top of the bin pointing downward so that it faces the material in the bin. The analog output from the sensor will need to interface with the PLC or computer so that the reading may be interpreted and any necessary functions may take place when the level reaches certain points.

Empty the bin and take note of the output from the sensor. Then, fill the bin to the maximum desired level and take another reading from the sensor. Now you have your high and low margins. You can program certain things to happen when the material hits a certain level, for instance, when the level of water in a bin reaches the top, the pump that supplies the water shuts off until the water is lowered again to another predetermined level.

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Ultrasonic sensors for level control

How to Measure Length and Diameter of an Object Travelling on a Conveyor

An application which requires an object to be measured for length and diameter as it travels along a conveyor belt may be solved using two types of sensors and a PLC.

Position a set of photoelectric sensors in a through-beam configuration so that the infrared beam crosses the conveyor. The object to be detected should break the beam as it travels. The photoelectric sensors will be used to measure the length of the object and also to trigger the measurement of the diameter by the ultrasonic sensor.

The ultrasonic sensor should be positioned above the conveyor facing downward and it should be well out of striking distance. The analog output from the ultrasonic sensor will be sent to the PLC, which should be programmed to calculate the diameter of the post based upon the sensor’s output.

The output from the photoelectric sensor actually serves two purposes. First, it will send a signal to the PLC indicating that the object is present. The PLC will then acknowledge the output from the ultrasonic sensor and begin its calculation. At the same time, the photoelectric sensors will help the PLC determine the length of the object using a calculation based upon the speed of the conveyor and the amount of time that the photoelectric sensors are blocked.

Though it sounds complicated, the hardest part of the application is the programming of the PLC, which should only be done by a trained professional. The benefits of using this equipment to solve the application are that the sensors are easy to install and they perform efficiently and reliably. Both measurements are done without physically contacting the object, so there are no moving parts to wear down.

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Infrared photoelectric sensors for conveyor applications
Infrared photoelectric multiplexer for mutiple sets of photoelectric sensors