Dynasonics 701_771C Series Insertion Ultrasonic Flow Meter - Manual (Page 34)

Rev. 12/97 -33- D77X
{2 nd FUNCT} SIGNAL STR
Displays the raw Doppler signal strength value. This
value will increase as the velocity of the liquid increases.
Typically, a liquid flowing at a velocity greater than 0.2
FPS [0.06 MPS], with adequate suspended solids (25 ppm
or 30 micron or larger solids) or aeration, will produce
SIGNAL STR readings over 150 counts.
NOTE: If the liquid is not flowing a low SIGNAL STR
reading is non-conclusive. If a high SIGNAL STR is
indicated at zero flow rate, it indicates that a source of
interference (another ultrasonic instrument, VFD, or poor
electrical ground) may be present. Verify that SIGNAL
STR increases when the flow starts. If it does, increase
the SS CUTOFF setting (see SS CUTOFF).
If SIGNAL STR is lower than 100 counts in a flowing
liquid, one or more of the following steps may need to be
invoked:
1. If the liquid velocity is less than 1 FPS (0.3 MPS) turn
SW-1 “LOW FLOW” switch ON. (This dual DIP switch
is located near the center of the Main PCB.)
2. If SW-1 did not cause an increase in SIGNAL STR to a
level above 100, turn ON SW-2.
3. There may not be adequate reflectors for the Doppler
principle to operate. The DT7 probe can be relocated
to a source of liquid degasification, such as would be
found a 1-3 diameters down stream of a 90-degree
elbow. A surrogate source of aeration can also be
introduced by bleeding a small amount of compressed
air into the line several diameters upstream of the DT7
probe.
{2 nd FUNCT} 4 mA
The 4-20mA output on standard D77 flow meters is scaled
PART 3 - KEYPAD CONFIGURATION