8.1 Measuring principle
This Guided Radar (TDR) level meter has been developed from a proven technology called Time
Domain Reflectometry (TDR).
The device transmits low-intensity electromagnetic pulses of approximately half a 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,
ε
r
, 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 emitted 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.
The illustration that follows shows a snapshot of what a user would see on an oscilloscope, if the
level of one product is measured.
Technology Solutions
Instruction Manual
Tek-Flex
4100A
8.
TECHNICAL DATA
www.tek-trol.com
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