Question

ultrasonic level transmitter

Discussion Questions: 1. Why would the temperature and the type of vapor in this vessel effect the accuracy of the ultrasonic level transmitter? 2. What is the purpose of the near and far blanking? 3. Explain "fail-safe" and "echo confidence". 4. What is the effect of reflection from obstructions in the vessel? 5. What is the effect of reflection from the surface at a low angle?

Answer 1

1.

Temperature and the type of the vapour in the vessel effect the accuracy of the ultrasonic level transmitter because the fluctuation of temperature affects the speed of an ultrasonic sensor's sound waves. As the temperature increases, the sound waves travel faster to and from the target. While the target may not have shifted, It will seem to the sensor that the target is closer. Air currents due to pneumatic equipment or fans may also deflect or disturb the path of the ultrasonic wave. This could lead a sensor to fail to recognize the correct location of a target and the pressurizing the vapour and types of vapour space above the level may affect. therefore the speed of sound may effect the accuracy.

2.

As we know that in order to understand the concept of blanking we should have the knowledge about ultrasonic sensors time and vibrations. The ultrasonics produces and detect vibrations. They pluse to produce a sound like speakers and listen for returning sound. Now, when the sound wave does return, it makes a small vibration on the face of the sensor. If is this second vibration that the sensor associate the required surface. The time, the return vibration is used to calculate the distance the sensor can then determine tank levels, volume, flow rate etc on a particular model and design. Therefore the period of waiting is called blanking distances. near means as little of 4 inches and far means as long as 1 to 2 feet or more.so it is used to calculate tank levels, volumes, flow rate etc.

3.Fail-safe:

The word fail-safe defines that when a loss of echo condition exists, the controller will indicate fail-safe and take any actions that have been pre-programmed for relays and other outputs

Echo confidence:

echo confidence defines that a measurement of the reliability of the current reading 100% indicates that the are no competing echoes. Lower values may indicate that the unit is choosing the best of two or more echoes.

4.

The effect of reflection from the obstruction in the vessel or tanks such as pipes, strengthening bars and agitators, may cause false echoes, but most of the transmitters will have the appropriate software programmes or algorithms to allow masking or neglecting of these echoes. so the effect of reflection from the obstructions in the vessel causes the echo problems.

5.

The effect of reflection from the surface at low angle causes target size and orientation, and the sensitivity setting of the sensor, for example, a sensor is mounted at low angle, the detection of undesired or off-axis objects can be affected. so it may effect the accuracy of the targets.

• I have reffered understanding ultrasonic level measurement (siemens) by stephen milligan. If you any doudt please refer that book
• I hope you are satisfied by the answer and understood well.