Xylem H-3553 - Manual (Page 21)

Setup & Operation
19
Bubble Rate
The bubble rate is the average number of bubbles flowing
from the end of the orifice line per minute. The standard
orifice line tubing that we recommend and calibrate the
bubble rate has 1/8 inch inner diameter (I.D.). If a different
size orifice I.D. is used the bubble rate will not be correct.
The bubble rate is a determining factor in the response
time of the H-3553 tracking a rise in stage. Table 4-12
Bubble rate response for 1 Ft. rise
30 bubbles/min 25 seconds
60 bubbles/min 20 seconds
120 bubbles/min 15 seconds
Table 4-12: Bubble Rate vs. Response Time
shows the approximate time needed to respond and track a one foot rise in stage with different bubble rates.
Note this is at a depth of one foot, at greater depths the time will increase slightly.
Another reason for changing the bubble rate may be to reduce noise in the data. Some sites have turbulent
water conditions creating water level data that looks jittery. The bubble rate may be changed, up or down, to
find optimal results to reduce this noise. Normally, it is a combination of changing the bubble rate and the
mean count/samples to produce the best results. The default values normally work best in the majority of the
applications and provide desirable results in a timely manner.
The H-3553 bubble rate default is set to 60 bubbles/min. The bubble rate range is 30 to 120 bubbles/min. To
change the bubble rate using the RS-232 main menu, press the ‘B’ key to enter the “Bubbler Settings” menu,
then press the ‘B’ key, enter in the new desired “Bubble Rate” and press the ‘Enter’ key.
To change the H-3553 bubble rate using the SDI-12 interface, send the “aXWBRnn!” SDI-12 extended
command. The response should be “a0061” which means that it could take 6 seconds to complete the
command and then it will put 1 data value in the buffer. To check the bubble rate and verify it was written
correctly send “aXRBR!” command and wait the responded time. Then send the “aD0!” command to read
back the new bubble rate. Note Table 4-13, the ‘a’ is the current SDI-12 address of the H-3553 and the ‘xx’ is
the current bubble rate of the H-3553 and the ‘nn’ is the desired bubble rate.
H-3553 Combo Bubbler setup menu sDI-12 Interface
B – Bubbler Settings Command: aXWBRnn!
: Response: a0061
Bubbler settings menu Command: aXRBR!
B – Bubbler Rate: xx Response: a0021
Enter Bubble Rate (30 -120) [ nn ] Command: aD0!
Response: a + nn
Table 4-13: Change the H-3553 Bubble Rate