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SMC sierra monitor corporation Sentry Instruction Manual - Version 6
CALIBRATION
Page: 47
5. CALIBRATION
5.1 SENTRY CALIBRATION - AN OVERVIEW
Calibration is a simple three step process:
1. Initiate calibration via the controller keyboard.
2. Apply zero gas (if required) and then span gas to the
sensors.
3. Close the calibration via the controller keyboard.
Calibration parameters are configured via the CHANGE
CALIB activity and are saved by Sentry for future calibrations.
During calibration Sentry "peak holds" the sensor signal output
for zero and span gas and then uses those values to construct a
curve for continuous reference during normal gas monitoring.
There are two alternative calibration methods, Global
Calibration and Local Calibration.
5.1.1 GLOBAL CALIBRATION
When Global Calibration is selected, the Sentry controller
collects zero and span value data from all sensor modules
eligible for calibration based on a global keyboard command. It
is not necessary to calibrate all the sensors, those which do not
receive span gas will be rejected automatically.
The operator presses the ENTER key to initiate, and complete,
collection of the zero value and then the span value. Calibration
gas may be delivered to the sensor module in a variety of
methods dependent upon the accessibility of the sensor.
The benefits of Global Calibration are:
• Magnetic calibration head not required.
• All "zero's" can be set at one time.
Global Calibration is particularly useful when:
• The sensor is in a position which is difficult to
access, because a calibration gas delivery tube can be
installed to a more accessible location.
• The magnetic head is not available or the magnetic
switch in one of the sensors is not functioning.
5.1.2 LOCAL CALIBRATION
When Global Calibration is turned off, the Sentry controller
collects zero and span value data from each sensor module
eligible for calibration based on a local command at the module.
Calibration gas is delivered through a magnetic fitting which
causes a switch in the sensor to command the controller to
remember the module output. The procedure calls for the
magnetic cap to be applied twice (zero first, span second)
except that the magnet is applied only once for oxygen modules.
The benefits of Local Calibration are:
• Individual modules can be calibrated while others
remain on line.
• Time savings when sensors must be exposed to zero
air due to the environment.
Local Calibration is particularly useful when:
• Plant operating procedures demand that some
modules remain on line while others are being
calibrated.
5.2 CALIBRATION INITIALIZATION
5.2.1 MODULES
Before any module can be calibrated it must be initialized via
the CHANGE MODULE activity. Initialization includes
turning the module on, setting the alarm levels and setting the
factor(s). This activity is described in step by step form in
Section 4.3 steps 6 through 18. If a module is not initialized, an
error prompt INITIALIZE MODULES FIRST will display
when calibration is attempted.
NOTE
The following calibration instructions are applicable to
controllers with version 6.xx firmware. For earlier
version firmware (example 4.2) refer to the Instruction
Manual furnished with that controller. To determine the
firmware version installed in any Sentry controller, press
TEST, ENTER and observe the firmware version number
on the lower LCD screen.
NOTE
If any sensors are not previously calibrated use
Diagnostic Code 0020 or 0021 to force calibration prior
to performing the normal calibration procedure. See
Section 8.3.5.