Appendix C
A-76
CALIBRATION
An important step in assuring accurate flow measurement is the proper calibration of the
instrument and the installation. This chapter provides an overview of the calibration
methods applicable to the DCT series of flowmeters. It covers the reasons why these
calibration methods are necessary, and the order in which they should be performed. The
calibration methods are:
!
Zero set calibration
!
Scale factor calibration
These calibration methods must be performed for the particular pipe that is to be metered.
Table 5-1 provides guidelines for selecting a calibration method:
Table 5-1
Selecting the Calibration Method
Calibration Method Function Application
Zero set calibration
!
Zero flow set
!
Manual zero set
Zeros the instrument for an
actual no flow condition
Applies a manually entered offset
to all flow readings
Installations where flow can be
stopped
Where an offset is required
Scale Factor Compensates for variations in
the inside diameter of the pipe
As required on installations
where the zero point has already
been set and verified under zero
flow conditions
NOTE:
The 4 to 20 milliampere (4 to 20 mA) current loop can also be calibrated for
applications using a current loop. Refer to Chapter 6 for more information.
5.1 Zero Set Calibration
Once the instrument is operating on the actual pipe to be metered, a small adjustment to the
zero point, or zero set calibration, may be required to maximize accuracy at low flow rates.
Zero set calibration allows the flowmeter to read very close to zero under zero flow
conditions.
There are two zero set calibration methods available in Menu 51: the zero flow set method
(Section 5.1.2) and the manual zero set method (Section 5.1.3). The zero point used in
either of these methods is displayed by selecting
MANUAL
in Menu 51.
NOTE:
After the instrument has been properly zeroed, it should display a stable reading
well below 0.05 feet per second (0.015 meters per second) under zero flow
conditions with the low flow cutoff disabled.
To Next Page
Loading...
Need help?
General