No two sensing technologies are built the same and what you have will have unique capabilities which dictate the area it should be used at. Do not hope for the correct reading when you have a photoelectric sensor in an environment full of dust because that interferes with the receiver. When you are in such an environment, you need an ultrasonic sensor because be it the sensing surface is full of dust or the air is musty and dusty your readings will be highly accurate. You will need such a sensor especially if you are working in the packaging, food and beverage and the agriculture industry. No matter what you need the ultrasonic sensor for, you should make the right choice. Think about the modes available in the sensor before you complete the purchase. Most of the sensors will have a thru-beam, diffuse and retroreflective beam. The most popular one is diffuse.
Once you are comfortable with the modes the sensor has, the next thing you ought to check out is the housing. They come in different materials, sizes and even shapes. In order to find the perfect one, consider your environment and the application. Many of the sensors you will find will have a flat pack housing, a cylindrical one or even one that is made in a cubic shape. The materials used in making the housing are either plastic or metal. If you want a sensor that is durable and can hold its ground in high torque, a metal one is the best. When you are working under favorable conditions, an ultrasonic sensor with a plastic housing will get the work done and there is no spending a lot of money in the purchase.
It is crucial to consider the output type because it has an effect on the kind of results you get. You can get a sensor with an analog output or switch point. Buy thinking about the job, you can know which output type will be preferable. The range of measurement of the sensor is something you should keep in mind too. If the sensor has a smaller transducer, the operating range will be small as well. The cost of the sensor is another matter you should have at the back of your mind. Do not assume that what is priced higher is the best thing for you but rather think of functionality and durability as well as the budget. It takes a bit of time but you will get the best item no matter the budget you have.