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Key Point:
In order to cancel any applied offset you must either read flow via
Quick
Start
or switch the Portaflow instrument OFF & ON. Any value that you trim-out
using the offset adjustment will be added/subtracted from the flow reading across
the whole range.
3.5.3 Adjusting the calibration factor
Key Point:
USE THIS FACILITY WITH CARE & ONLY WHERE NECESSARY
The Portaflow instrument is fully calibrated before leaving the factory and under
normal circumstances does not require further calibration when used on site.
This facility can be used to correct the flow indication where unavoidable errors oc-
cur due to the lack of a straight pipe or where the sensors are forced to be fitted
close to the pipe-end, valve, junction etc.
Any adjustment must be made using a reference flowmeter fitted in the system.
With the system running:
1. Stop (Stall) the Portaflow’s totaliser facility and zero it
(Paragraph 3.6.1
).
2. Run the Portaflow’s totaliser to measure the total flow over a 30-60 minute period, and note the total flow
indicated by the reference flow meter over the same period.
3. Calculate the % error between the Portaflow and reference meters. If the error is greater than ±1% calibrate
the Portaflow as detailed below.
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
Totaliser
:
Run
Reset +Total
Reset –Total
Calibration factor
:
1.000
Roughness factor
:
0.01
Diagnostics
Exit
4. Press the Options key to access the FLOW
READING OPTION screen shown.
5. Scroll down and select Calibration factor.
6. Change the calibration factor according to the error
calculated in step 3. For example, if the Portaflow
was reading 1% high then increase the Calibration
factor value by 0.010. Conversely, if the reading is
1% low then decrease the calibration factor to
0.990.
7. Press Enter to apply the change.
8. Select Roughness factor or Exit as required.
3.5.4 Adjusting the roughness factor
The roughness factor compensates for the condition of the internal pipe wall, as a rough surface will cause
turbulence and affects the flow profile of the liquid. In most situations it is not possible to inspect the pipe
internally and the true condition is not known. In these circumstances experience has shown that the following
values can be used: