Contact Level Meters – Measuring principle TDR

The Guided Radar (TDR) level meter has been developed from a tried and tested technology called Time Domain Reflectometry (TDR). The device transmits low-intensity electromagnetic pulses of approximately one nanosecond width along a rigid or flexible conductor. These pulses move at the speed of light.

When the pulses reach the surface of the product to be measured, the pulses are reflected with an intensity that depends on the dielectric constant, εr, of the product (for example, water has a high dielectric constant and reflects the pulse back to the meter converter at 80% of its original intensity).

The device measures the time from when the pulse is transmitted to when it is received: half of this time is equivalent to the distance from the reference point of the device (the flange facing) to the surface of the product. The time value is converted into an output current of 4...20 mA and/or a digital signal. Dust, foam, vapor, agitated surfaces, boiling surfaces, changes in pressure, changes in temperature and changes in density do not have an effect on device performance.