KROHNE optiplex 1300 c, Руководство пользователя

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Handbook OPTIFLEX 1300 C
87 OPTIFLEX 1300 C
The waveform below the diagram shows a snapshot of what the user would see on an oscilloscope.
TBF mode
Level measurement
This measuring mode is used when an insufficient amount of EM pulse energy is reflected back from the
product surface (dielectric constant < 1.6). Most of the pulse is reflected back from the probe end.
This mode uses the principle that while not much of the pulse is reflected, the speed of the pulse changes
as it goes through different media. For example, the speed of light in a product such as oil is lower than the
speed of light in air.
If the time it takes for the pulse to reflected back from the probe end when the tank is empty is known, then
the level can be calculated.
The difference between the time it takes for the pulse to be reflected back from the probe end when the
tank is full or partially filled and the time it takes for the pulse to be reflected back from the probe end when
the tank is empty is proportional to product level.
The diagram below shows how TDR works when the device is configured to measure the level of a product
with a low dielectric constant.
Empty tank
At time, t, represented by a vertical line, the following occurs:
•
t0: EM pulse emitted.
•
t1: Pulse travels down probe at the speed of light in air, V1.
•
t2: Pulse reflected back from probe end.
•
t3: Pulse travels back to the receiver at speed, V1.
•
t4: The receiver receives and records the level return signal.
Partially-filled tank
At time, t, represented by a vertical line, the following occurs:
•
t0: EM pulse emitted.
•
t1: Pulse travels down probe at the speed of light in air, V1.
•
t2: Pulse travels down probe through the product at speed
•
V2.
•
t3: Pulse reflected back from probe end.
•
t4: Pulse travels up probe through the product at speed V2.
•
t5: Pulse travels up probe at the speed of light in air, V1.
•
t6: The receiver receives and records the level return signal.