GE TMO2D, User Manual

Page: 50 / 102

Chapter 4. Basic Programming
42 TMO2D Digital Display User’s Manual
4.8.5 Auto Cal Parameters
You can program the TMO2D to perform an automatic calibration procedure (Auto Cal) at specified time intervals
ranging from minutes to months.
By performing measurements on either one calibration gas (offset or span) or on two calibration gases (zero and span),
the unit can correct for changes in the response of the transmitter without operator intervention.
At the specified time interval, the TMO2D activates a solenoid valve on a sampling system using one of the relays
provided. This procedure isolates the transmitter from the process stream and connects the transmitter to one of the
calibration gases. After a programmable time, during which the calibration gas replaces the process gas, the transmitter
takes measurements of the calibration gas.
The analyzer then activates a second solenoid valve, using a second relay, to connect the transmitter to the other
calibration gas. The transmitter then equilibrates as the second calibration gas replaces the first gas, and takes
measurements of the second calibration gas.
After taking span and zero gas measurements, the TMO2D reconnects the transmitter to the process stream. Then a
final settling time takes place while the process gas replaces the calibration gas.
Once settling has been completed, if no error has occurred, the analyzer calculates the amount of drift and applies the
calculated drift to the factory calibration data. The factory calibration data remains unchanged. The TMO2D stores the
corrections to the calibration data as the Drift Curve.
If the Auto Cal measurements are beyond the preprogrammed limit, the unit disregards the data and uses the drift curve
already stored in memory. If you have enabled Auto Cal Error Handling (see page 47), the display and outputs will
respond as programmed. If any alarm relays have been assigned to trip on Auto Calibration Errors, they will be tripped.
Contact the factory to expand the AutoCal drift limits. The default limits are 25% of full scale per calibration and 40%
of full scale total drift.
Alternately, the automatic calibration can be performed in an offset or span correction manner using a single calibration
gas and one solenoid valve. When calibration is active, the autocalibration status replaces the display of pressure or
background:
•
Cal:ok (no errors and no new cal data applied)
•
Cal:new (no errors and new data applied)
•
Cal:err (total or per reading drift error)
Follow the steps below to enter the Auto Cal Parameters submenu.
CALIBRATION MENU
Auto Cal Parameters? Press [YES] to enter the Auto Cal Parameters submenu.
Enable AutoCal:
[YES] no
Press [YES] to enable the AutoCal function.