Dwyer UFB - Manual (Page 25)

3: Operating Procedures
21
3.3 Instrument Calibration
The instrument 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 applications where necessary. Apart
from the ‘zero flow offset’, these adjustments are normally carried out only where the instrument is to be used at a
permanent, or semi-permanent, location.
3.3.1 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 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 (password required).
2. Select Zero Cutoff (m/s) and press
ENTER.
3. Enter the value for the Zero Cutoff (e.g. 0.06
m/s) then press ENTER.
4. Scroll down to select Exit and press ENTER to return to the FLOW READING screen.
3.3.2 Adjusting the set zero flow offset
The UFB 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
±0.005m/s (possibly higher on smaller diameter pipes). If a greater figure is shown, it is worth cancelling the
offset to obtain a more accurate result. Continue as follows:
3. Press the Options key to access the FLOW
READING OPTION screen shown.
4. Select Set zero flow (m/s) and press
ENTER.
5. Press ENTER on the subsequent screen to
accept the change, which will return you to the
screen shown.
6. Scroll down to select Exit and press ENTER to
return to the FLOW READING screen.
Key Point: 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 cancelled you can
then reapply the Zero Cutoff if required.
FLOW READING OPTION * *
Data review
Zero Cutoff (m/s) : 0.100
Set zero flow (m/s) : 0.000
Damping (secs) : 10
Totalizer : Run
Reset +Total
FLOW READING OPTION * *
Data review
Zero Cutoff (m/s) : 0.010
Set zero flow (m/s) : 0.000
Damping (secs) : 10
Totalizer : Run
Reset +Total