ATI Model F12/D Gas Transmitter Part 4 – Operation
40
O&M Manual (Rev-H)
Sensor Calibration
Calibration Frequency
While the transmitter itself requires no periodic calibration, H10 sensors should be “zero” and “span”
calibrated every 3-6 months, based upon environmental factors. Sensors frequently exposed to dirt, oil
mist, vapors, or very dry air, may require more frequent calibration.
Zero Calibration
As the name implies, zero calibration corrects the transmitter offset reading in the absence of any reactive
gas. During zero calibration, the offset error is stored in the sensor, and subsequently subtracted from
future readings. ATI recommends bottled zero gas as a source, which should be selected based on the
type of sensor. For example, bottled “Zero” Air may be used to zero Chlorine sensors, but Oxygen sensors
require bottled Nitrogen gas.
Span Calibration
Span calibration corrects the transmitter sensitivity to a known concentration of target gas (the gas for which
the sensor was designed to monitor). Sensors for most gases, such as Ammonia, require a bottled “span
gas” source. This applies even to Oxygen sensors, where the span gas source is bottled zero air.
Calibration Terminology
The zero calibration is referred to as, “zero”, “zeroing”, and “zeroed”. Likewise for the span calibration,
which appears as, “span”, “spanning”, and “spanned”. As with most instruments, zero calibration should
be performed before span.
Calibration Kits
Calibration kits, containing zero and span bottle gas sources, are available from ATI for many toxic gases.
Contact ATI, or your local ATI representative, if you have questions about calibration gas kits or gas
sources.
Indications During Calibration
The “un-blanked” gas concentration value is displayed during zero and span calibration, primarily to observe
any slight amount of positive or negative drift. Alarms are cleared and inhibited, and the 4-20mA output is
locked at 4.0mA (transmitters equipped with Oxygen sensors are locked at 17.4mA, representing normal,
20.9% atmospheric Oxygen). The 4-20mA output will not change when gas is applied and removed, and
for 15 minutes thereafter (the default value). While viewing the calibration pages, the LCD display will
indicate the changing gas concentration.
Calibration Exceptions
Zero and span calibration are not allowed during the following conditions:
Sensor removed, or in 5-minute
warm-up period
Trouble alarm active
Auto-test active (status indicator appears on Main Display page)
To help prevent errors, zero and span are not allowed if the sensor output, or span value entered, is too
high or too low. If detected, memory errors are reported while updating the sensor or transmitter memory.
Typical value, may vary by sensor gas type.
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