51-638 Echotel Model 338 Two-Wire Ultrasonic Transmitter
14
P05:
Dead Zone
Factory default value for P05 is: 10.0 inches
Non-contact ultrasonic transmitters require a "dead zone"
or "blind space" between the face of the transducer and
the maximum liquid level. The minimum dead zone for
the Model 338 is 10" (25 cm), as shown in the drawing at
left. The 338 will not process any ultrasonic signals within
the dead zone. For this reason, it may be necessary to
mount the transducer in a standpipe to enable the 338
to measure all the way to the top of a tank. Refer to
Section 1.2.5, Standpipes,
for information on mounting in
standpipes.
For most applications the factory default value of 10" (25 cm)
is used, which allows the unit to have the smallest possible
dead zone. Entering a value larger than 10" (25 cm) allows
the unit to block out any false echoes originating from the
bottom rim of a standpipe, or from any object protruding
into the ultrasonic beam close to the transducer. Since the
338 will not measure any value inside the dead zone, the
full tank (usually 20 mA) value will need to be adjusted if
the dead zone value is changed.
P06:
Far-end Blocking
Factory default value for P06 is: 00
Level or Volume Applications
Far end blocking is used to ignore false reflections caused
by objects at the bottom of the tank. This can be helpful
with tanks that have heaters, or other objects at the bot-
tom of the tank, and also with conical bottom tanks
where level measurement may not be necessary below a
preset level.
P06 is entered as the distance from the bottom of the tank
to top of the interfering object. If the liquid level falls
below this preset level, and enters the far end blocking
section of the tank:
1.
"Sub 0"
will be shown in the LCD
2.
"FAIL"
will blink on/off
3. The mA output will hold the value that corresponds to the
far end blocking level
Range (P04)
Dead Zone (P05)
Far End
Blocking (P06)
DIST=distance (measured)
LEV=level (P04-DIST)
Span
(P04-P05)
