The Mabat Silt Density Index 2200 can measure the SDI in two modes:
Standard Test Mode
This mode is suitable for high-quality water, when the expected SDI value is lower than 5 for a 15 minute Check Time.
The cycle is continued until the Check Time (1-15 MIN) is done, disregarding the Plugging Percentage.
The disadvantage of this mode is that, in case of high SDI ( >5), the filter might be completely plugged.
In this case the cycle will be terminated, without any calculation. The value for Tt in the formula is always the programmed for the Check Time.
This mode can be used for high SDI water, only after decreasing the CHECK time to any value between 1-15 minutes. In this case, the programmed CHECK time should be reported with the SDI results.
Auto Time Test Mode ( SDI 75% )
This mode is preferred when the water quality is low (standard SDI >5), or when quality fluctuation is expected.
The cycle is continued until one of the following conditions is met:
- The Plugging Percentage is greater than the pre-set value (75%).
- Check Time has expired.
The plugging percentage is calculated and displayed every one minute.
The value for Tt in the formula for the first case (75% ) is the time in minutes, when the plugging exceedes the set point.
The value for Tt in the formula for the second case is the Check Time.
The advantage of this mode is that the filter paper is never fully plugged and the cycle is always completed with a calculated result.
The SDI results are presented on a 0-100 scale, and the exact CHECK time has no meaning as in the Standard Test Mode.
In general, the higher the SDI result the more silt is in the water.
The Plugging Factor is calculated using the formula:
%P30 = 
Where:
%P30: Plugging factor at 30 [psi] feed pressure,
Ti: Time required to collect the first 100 cc of sample,
f: Time required to collect 100 cc of sample after each minute.