Cutting off measured values

According to EN 15267-3, it is allowed to cut off high emissions. This prevents a few measurements from destroying the hourly average. This is an excellent feature that can be used on all primary AMS measurements.

Over time, some plant owners with AMS equipment have benefited from maintaining their hard-wired connections between AMS equipment and data collection due to the natural limitations of the 4-20mA communication form. This limitation is based on the fact that the measurement interval is often distributed over the 4-20mA, in order to obtain the best possible resolution and thus maximum precision on the measurements. A natural consequence is that the signal saturates outside the measuring range and therefore does not go beyond 20mA. The scenario changes when measuring emissions via bus technology. Here, the entire range of the analyser can be utilised as bus signals do not get saturated. As a consequence, very high measurements are included in the hourly averages which can result in exceeding the environmental values.

ReportLoq incorporates a feature that offsets the difference between hard-wired and bus connections, which means that bus technology can be used without the high measurements causing problems.

Cutting off 2% of all measurements are allowed according to EN 17255-1 Annex C. Plant owners with hard-wired data collectors must therefore flag the measurements that result from the analyser being saturated. Plant owners with bus technology systems can, in turn, cut off the measured values ​​in the environmental reporting system as long as they meet the same 2% limit. The rule thus offsets the difference between analog and digital systems.

The cut-off can be carried out on all measured components and can result in significant reductions in installations with high fluctuations on primary emission values.

Cut off level

The EN 15267-3 describes that

  • Waste incineration plants use at least 1.5 x daily limit value
    Recommendation 3 x daily limit value

  • Large combustion plants use at lease 2.5 x daily limit value
    Recommendation 5 x daily limit value

  • No plants may cut off more than 2% of their measurements per month

In practice

As described, signals can be cut off in ReportLoq. When purchasing “cut off”, an analysis of the previous month’s measurements is included which ensures that the 2% limit is met. This avoids setting the limit too low which may mean adjusting the limit with subsequent recalculation of the month, as described in EN 17255-1.

Plant owners with hard-wired meters can also purchase cut-off. Here, the cut-off limit will be set immediately below the saturation range of the signal. Thus, cut-off values are flagged according to the rules, and the number of cut-offs caused by the saturation of the signal can then be calculated.

In both cases, the amount of cut values will be calculated in the cut-off report provided. This acts as the plant’s documentation for compliance with the described 2% limit. An example of the report can be found in the Report Summary.

But isn’t that cheating?

One could argue that cutting off the measured values is an artificial reduction of emissions. However, it is important to keep in mind that the cut-off limit is substantially higher than the limit value, and in conjunction with the requirement of a maximum of 2% cut-off in one month, this means that cut-offs can only be used to a limited extent and still gives high emissions during use. Cutting thus becomes a tool to prevent abnormally high readings from destroying the hourly value over a few seconds.

Share this article