REFLECTOMETER
50
5.4.2. SHORTENING FACTOR SETTING
For the correct operation of the REF, it is necessary to set a Shortening Factor (a characteristic
showing how many times the phase or group wave velocity in the cable is less than the speed of
light in vacuum).
The Shortening Factor depends on the type of wire, the size of its cross section and the
electromagnetic parameters of the material from which the wire is made (capacity, inductance).
Sometimes technical documentation uses Velocity Factor (VF) also called Wave Propagation
Speed or Velocity of Propagation (VoP) instead of a Shortening Factor. The values of these factors
are indicated in reference books, cable specifications or on the Internet.
If only the Velocity Factor (Velocity of Propagation) is known, it is necessary to calculate the
Shortening Factor according to the following algorithm:
1. The Velocity Factor value specified in % is transformed to decimal shares.
2. The inverse of the obtained value is calculated.
For example:
Velocity Factor=60% (0.6). Shortening Factor = 1.67 (inverse value from 0.6).
The Shortening Factor equal 1.5 is by default set (corresponds to Shortening Factor of a two-
wire SQR-2 cable). For setting of Shortening Factor it is necessary to press "F2". The dialog
window (Fig.52) will appear.
The value of Shortening Factor is present in the "X.XX" format. Movement of a marker is
made by means
or buttons. Setting of value is made by means
or
buttons.
After setting of Shortening Factor for exit to the REF main menu it is necessary to press "F2",
"ESC" or "ENTER".
Fig.52
The new Shortening Factor value will be display in the "F2" field (Fig.51, item 4). This value
remains unchanged until the next setting or power off.
5.4.3. AUTOMATED MODE
AUTOMATED mode is used when testing a multi-wire cable. Measurements are made
sequentially for each combination of wires.
To turn on the mode, in the REF main menu, press "F4" ("Scan All"). The tabular cursor is set
to one of the rows of the table (Fig.51). Measurement begins. In the "Level/Dist" cell, "running
points" appear.
