Process / measurement point
Temperature, moisture, dust, pressure and the flow profile in the duct affect the conditions for sampling. The position of the measurement point relative to the process geometry and its variation affects whether the sample is representative. ARKTEC starts from the existing measurement point and takes its conditions into account when assessing the rest of the measuring chain.
Sample extraction / sampling
This is where the sample gas is extracted from the process. Probe, filter, heating, gaskets, leak-tightness and sample gas flow affect which sample is actually passed on through the system.
Leaks or damaged gaskets can let in ambient air — air ingress — which dilutes the sample gas and changes the measured concentrations. Filter loading or insufficient temperature can at the same time affect the flow and the composition of the sample.
Sample line
The sample gas should reach the next stage with as little unintended change as possible. Temperature drops, leaks at joints, transport time and condensation can affect the sample before it reaches the sample conditioning or the analyser.
In heated systems, the correct temperature and unbroken heated zones are essential to avoid cold spots and unwanted condensation. Low points where condensate can collect also need attention.
Sample conditioning
Sample conditioning adapts the sample gas to the requirements of the analyser and its measuring principle. Depending on the system, this can involve filtration, cooling, drying, condensate removal and control of the sample gas flow.
Coolers, filters, pumps, condensate drains and flow control affect both the condition of the sample and the response time of the system. Where relevant, the leak-tightness of the system is included too.
Analyser
The analyser measures the sample gas that reaches the instrument. Measuring principle, instrument response, sample gas flow, cross-sensitivities and drift over time can affect the displayed value.
Zero and span checks, reference gas and instrument status are used to monitor the analyser’s performance. How much of the chain the check covers depends on where the reference gas is injected: at the analyser it says little about the sample gas path, at the probe more — but nothing about how representative the sample is.
What looks like drift or instability in the analyser can sometimes have its cause earlier in the chain, for example in flow, leaks, filter loading or sample conditioning.
So the analyser can be working correctly while a fault exists earlier in the measuring chain.
Signal & data
The value the analyser sends should match the value the receiving system reads. ARKTEC can check this, for example by comparing a known output signal with the recorded value. Scaling, analogue or digital transmission, units and status information affect how the signal becomes stored measurement data.
A correct instrument value can become wrong in the next system if the signal is scaled, mapped or handled incorrectly.
Reported result
The reported result is the end product of the measuring chain. Calculations, conversions to reference conditions and reporting are done in the site’s emissions reporting system, which is often supplied and maintained by an external vendor.
ARKTEC does not perform these calculations. We track the result: relevant results and status — for example whether an external test passed or showed a deviation — are entered in the installation’s technical history and used as context at future inspections.
The reported result is therefore the result of the entire chain — not just the analyser’s measurement.
A stable value is not automatically a correct value.
An error can be stable over time. That is why the measured value needs to be assessed together with the technical condition of the rest of the measuring chain.
MEASUREMENT ASSURANCE & DOCUMENTATION →SEE OUR SERVICES