Dwyer Series PUB - Manual (Page 23)

3: Operating Procedures
19
3.4.2 Changing a site name
To change a site name, use the same method described above for generating a new site: but in this case select a
current site name to change rather than an
EmptySite.
3.5 Instrument Calibration
The PUB is fully calibrated before it leaves the factory; however the following adjustments are provided to allow
you to further ‘fine tune’ your instrument to suit local conditions and application where necessary. Apart from the
zero flow offset adjustment, these are normally carried out only where the instrument is to be used in a permanent
or semi-permanent location.
3.5.1 Adjusting the zero cut-off
This adjustment allows you to set a minimum flow rate (m/s) below which the instrument will indicate ‘0’. The
default setting is 0.1 m/s (0.033 ft/s) but you may adjust this value if required.
1. With the instrument operating in FLOW READING mode, press the Options key to access the FLOW
READING OPTIONS menu shown.
3.5.2 Adjusting the set zero flow offset
The PUB instrument operates by comparing the time taken to send an ultrasonic signal between two transducers
in either direction. A
Set zero flow offset adjustment is provided to compensate for any inherent differences
between the two sensors, noise pick-up, internal pipe conditions etc. It can be used to ‘zero’ the flow indication
under no-flow conditions.
1. Stop the liquid flow.
2. With the instrument in FLOW READING mode, press the Velocity function key and observe the reading
(m/s). Any reading other than 0.000 indicates an offset error and in practice this will typically be in the range
±0.005 m/s (0.0016 ft/s) – possibly higher on smaller diameter pipes. If a greater figure is shown, it is worth
calibrating the offset to obtain a more accurate result. Continue as follows:
2. Select Zero Cutoff (m/s) and press the
ENTER key.
3. Enter the value for the Zero Cutoff (e.g. 0.06
m/s) then press the ENTER key.
4. Scroll down to select Exit and press the ENTER
key to return to the FLOW READING screen.
FLOW READING OPTION DD-MM-YY HH:MM:SS
Data review
Zero Cutoff (m/s) : 0.00
Set zero flow (m/s) : 0.00
Damping (secs) : 10
Totalizer : Run
Reset +Total
If you have adjusted the Zero Cutoff point to anywhere above ‘0’ you must reset it to
‘0’ before you can observe and adjust the Set zero flow offset, as its value is very
small. Once the Set zero flow offset has been calibrated you can then reapply the Zero
Cutoff if required.