KROHNE optiplex 1300 c, Руководство пользователя

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Handbook OPTIFLEX 1300 C
OPTIFLEX 1300 C 86
8.2 Measuring modes
General notes
This level meter can track product level using three measuring modes
Mode Description
Automatic The device determines automatically which is the most suitable mode
(direct or TBF) for measuring
Direct Measurement is made from the reflection direct from the product surface
Tank bottom following (TBF) Used for products with low dielectric constants, by measuring indirectly
using the reflection from the probe end
Direct mode
Level measurement
This is described in the general principle.
Level and/or interface measurement
The interface distance can be measured when the top liquid has a lower dielectric constant than the one
underneath.
The residual pulse left over from the reflection from the top liquid surface continues down the probe and is
reflected from the interface. The top liquid's dielectric constant determines the speed of the electromagnetic
pulse through the top liquid.
The distance to the interface can be calculated by the device if:
•
the distance to the top product surface and
•
the top product's dielectric constant
are known.
The layer, defined as the depth of the top product to the interface, must be at least 50 mm or 2" for the
device to accurately calculate interface distance.
The diagram below shows how TDR works when measuring the level of two products. 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: Part of pulse reflected back from top layer back to receiver, the rest of the pulse continues through
the top product.
•
t3: Part of the pulse travels back to the receiver at speed, V1, while the rest of the pulse continues down
probe through the top product at speed V2.
•
t4: The receiver receives and records the level return signal. The rest of the pulse continues down
probe through the top product at speed V2.
•
t5: The rest of the pulse reflects from the interface.
•
t6: The rest of the pulse travels back through top product at speed, V2.
•
t7: The rest of the pulse travels through air at speed, V1.
•
t8: The receiver receives and records the interface signal.