14
SafeGuard Controller User Manual
MAN-0115 Rev 0
2.2.7 CAL
MODE
This SafeGuard Controller feature is only accessible when
Sensor Direct
or
Analog
Input with Local Cal.
is selected. The
Analog Input with Local Cal.
option may be used
if the transmitter and sensor connected to the controller are located in an area not easily
accessible. A calibration tube should be fitted to the sensor and run to an easy access
location where a gas canister is fitted and calibration performed using the calibration
menu. It should be noted that the current output from the SafeGuard Analog Output
Board will be 1.5 mA when the device is in calibration mode.
The CALIBRATION MENU allows entering the correct
Cal ZERO
&
Cal SPAN
set-
point values needed to calibrate the sensor. These are entered in the same engineering
units as input range.
Set Zero
&
Set Span
controls in this menu allow pushbutton
calibration by moving the pointer to each and pressing the
EDIT
key. A live reading of
the channel’s value allows calibration checks to see if an adjustment is needed.
Unintentional calibrations are reset by the
Unity Gain
menu item.
Unity Gain
resets
zero offset to 0 and span gain to 1. It is useful for returning the calibration to a known
starting place. Sensor aging may be monitored by recording zero and span readings at
Unity Gain
when it is new, and again at later dates when degradation may have
occurred.
To check zero calibration, apply the ZERO calibration value to the sensor and observe
the live reading. If the zero reading differs from the zero setpoint, a calibration is needed.
To calibrate zero, move the pointer to
Set Zero
and press
EDIT
. A warning message
explains that pressing
EDIT
again will change the zero calibration and any other key will
exit. The procedure for span calibration is identical. For example, if an LEL combustible
sensor is to be spanned with 50% LEL span gas, the span set-point must be 50%. If 45%
LEL is to be used later, the span set-point must be changed to 45% to match the span
calibration gas. If the reading is only 40% LEL with the 50% gas applied a span
calibration is needed. Move the pointer to the
Set Span
entry and press
EDIT
twice.
Unity Gain
may be used at anytime to cancel incorrect calibrations and start again. See
Figure 2.8.
Figure 2.8
