No need to touch
Non-contact radar level measurement – an overview

Historically, users have stayed away from non-contact radar, due to price and difficulty or complexity of use. The latest generation of devices has sought to address issues of high cost and complexity – to put non-contact radar on a level playing field with other methods.

An investigation of non-contact radar level transmitters yields acronyms such as FMCW and PTT – describing different types of non-contact radar. FMCW (Frequency Modulated Continuous Wave) is a technique that is somewhat complex (using Fast Fourier Transform analysis), a more expensive device historically used in inventory applications. It often requires line power to be run directly to the transmitter, and a separate pair of wires in a separate cable to carry the signal back. This can become expensive to install.
Hence the popularity of loop-powered radar, which uses only one pair of low voltage wires to carry both power and signal. These are usually PTT (Pulse Transit Time) devices that can even be installed intrinsically safe, eliminating the need for expensive explosion proof cable all together. Pulse devices are gaining popularity due to their relative simplicity and cost effectiveness.

A loop-power device has only about 3.5 mA (24 VDC) of power to work with, and non-contacting radar (unlike GWR) loses a significant amount of energy to beam spread. There are two basic approaches. One is to operate the device intermittently to save power. This is sometimes called duty cycling, or interval operation. This approach does save energy, but can limit speed of response and the ability to handle fast changing levels. Another approach is to use PTT (Pulse Transit Time) combined with the latest impulse radar, and ETS (Equivalent Time Sampling) signal processing techniques, so the device can monitor your process continuously even during rapid level movement.
A note on safety: Many non-contact radar units are extremely safe to use, operating at such low power that they need no license. For example on Magnetrol’s Pulsar, output at the antenna has a peak of 2 mW. This is hundreds of times less energy than is emitted at the antenna of a cell phone.
In summary, here are some significant features to look for:
Quick connect/disconnect fitting makes installation a snap
Antennas are interchangeable
Unit can be removed while leaving vessel sealed
Simple, linear menu makes configuration simple
False Target Rejection is simple, intuitive and effective
Simplicity makes PC software unnecessary
Ability to track fast moving level changes