DDS tutorial 14 - Threshold parameter

The threshold is a parameter, which is used in online systems.

The threshold idea came from vibration measured on hydroelectric turbines. Such machines are not running continuously. The turbines are run and stopped several times every day. And we want to save just running values.

When such intermittent machine is turned off there remains noise values, which we don’t want to save. It means, when the values are lower than the threshold value, we do not save them.

When the measured value is above threshold, then the machine is running. When the measured value is bellow, then the machine is not running. To set the threshold correctly is important.

How to choose the threshold value? Threshold value has to be lower than normal machine vibrations and higher than noise value.

It means if normal machine vibration is 2 mm/s and noise value is 0.2 mm/s than the threshold value should be set for example to 0.5 mm/s.

Where you set this value in DDS? Open DDS software. Open your online database. Go through the tree to data cells level. Click on measurement data cell with right mouse button. Choose Properties. Go to online tab.

You can see saving section here. There is parameter named Min value threshold. This parameter stands for the threshold value. Click to the field next to Min value threshold name. Fill in your chosen threshold value. You can decide that this data cell threshold value will be set for the whole machine. All data cells on this machine are still measured but they do not save the data. Machine is considered as not running. Until this one data cell - marked as threshold data cell - measures values higher than set threshold. From that moment values are saved in all data cells according to data saving parameters set.

 Once the threshold is set, it is important to start the measurement again or to press the continue button.

From now – values below the threshold will not be saved. Unless.

There is one exception. Adash threshold is smarter.

When value decreases below the threshold this first value is saved. Now you know that you are in not running vibration values. Next ones below threshold are not saved. Unless the values go up and get above the threshold. The last value before we get again above the threshold is saved also.

Keep in mind that threshold parameter should be used only for machines which are not running continuously. It is also important to choose proper value as a threshold value.