"Time Constant" and "Backup" for Analog input in Menta

[Makarand988]

Hi

I am using schneider SHD100 -T Temperature + RH sensor 

I am curious to know about the "Time Constant"  and "Backup" in Analog Input.

Information is there in Menta Web help but I didnt understand.

If I keep it too high for example 100 sec, so what will happen ?

What value should I consider as rule of thumb for "Time Constant" ?

Does it affect the accuracy of the sensor ?

What does mean by "Backup" check box while creating analog input in Menta.

[MikaelKrantz · Accepted solution]

First the Backup.

This is to be able to store the value over a power failure.

However, if you use it for reading a sensor, it will read the actual value of the sensor, so no use in this scenario. 

If the AI block is set as Constant value, then you may select the Backup flag.

Time Constant

This is a first order filter to make it possible to slow down rapid changes. 

Should use like 5 or 10 seconds, depending on what type of signal you are reading, others may use other values.

Could be used like noise reduction...

[Makarand988]

Hi

Please refer below snap from the data sheet of SHD100-T. Does it indicate that should I use Time Constant = 15 Sec

[MikaelKrantz]

Well, you can use 15 seconds as well.

However that value is for the sensor, how long time it takes for a change of temp to affect the value...