Service and Maintenance Installation and Operation Manual - COMTEC
®
/
OXITEC
®
DustEx
16 Doc.-ID: COM_OXI_Dust_11022020
5.12 Digital Inputs
The digital inputs are designed for a direct voltage of 12 V - 24 V DC for logical “High”. Logical “Low” corresponds to
a voltage less than 1 V.
Digital input Function
Calibration release External release for calibration with ACAL
Measuring range switch Switching on the second measuring range
5.13 Stability Criteria for Calibration
During calibration, the cell is checked for stability. This check operates according to the following criteria.
The last measured value is always temporarily saved. When the next value is outside the tolerance, the internal timer
is reset and the new value temporarily saved. This means that if the timer was not reset, the value is stable. In this
way, the last measured value after the timer has elapsed (2 min.) is used to calculate the cell constant or slope.
5.14 Reaction Time of the mA Output
The reaction time of the mA output to a change of the O
2
cell input voltage is less than 200 ms.
5.15 Extension Modules
As an option, the electronic unit is available with several interfaces (RS232, RS485, HART, Fieldbus). If one of these
options is ordered you will find a separate manual/specification for the respective interface together with the
shipment.
5.16 Maintenance Intervals
In general, maintenance as well as the maintenance intervals always depends on the flue or process gas conditions
in which the probe is installed. Maintenance intervals may therefore vary between a few months up to a few years.
The biggest influencing factors are the presence of corrosive ingredients such as SO
2
or HCl, a continuous reducing
atmosphere (reduced oxygen concentration, increased levels of combustibles) and the characteristics of the solid
components in the flue gas.
These may have the following effects: chemical or mechanical destruction of the probe, clogging of the filter element
or accelerated aging of the sensor. This may lead to a distortion of the measured values as well as an increase in the
response time, which can in turn lead to false process operation afterwards.
For this reason, a sensor check is recommended with test gas and test air every six months. If a significant deviation
between the values obtained and those presently anticipated, a 2-point calibration should be carried out. A visual
inspection of the probe should be conducted at least annually, which includes cleaning of the filter element if
necessary.
Notwithstanding these recommendations, the operator must define an appropriate maintenance interval which
reflects the criticality of the measurement and the process.
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