11 Top Blowdown
Mk8 MM Manual Page | 216
11.6.4 Sample Routine
The time for one complete measurement cycle is 3 milliseconds. It can be seen that 10 measurement cycles
are made within one second. These measurements are averaged over one second. Conductivity is
calculated by dividing measured milliamps by 0.5 volts which gives a value in micro-siemens.
At the start of each measurement cycle the sample is checked for polarization. This background voltage
effect is taken into the conductivity calculations.
Temperature and pressure are measured by the Autoflame system and this information is used to continually
modify the calculated conductivity/TDS value from its calibrated point. Nominally for every 1°C increase or
decrease, 2% is added or subtracted from the conductivity value. The exact figure is calculated by the
system.
The system relates conductivity in micro siemens to TDS in ppm by a 0.7 multiplier. Within the control
software there is an adjustment of ± 7% for this multiplier which is user variable.
The TDS system logs each of the samples within the 1 second time period. It takes all 10 sample values,
adds them together then divides them by 10 to obtain the average TDS value for the one second period.
Once the TDS software has calculated the average TDS value for the 10 samples within one second, it will
then extract these averages and add the last 10 together and divide them by 10 to give the actual TDS
reading. This value will be displayed on the M.M.
When a new average of the 1 second samples is obtained, the software will utilise the last 9 averages, it will
then add the new average to them and divide it by 10 to obtain the new TDS value.
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