TIA Portal V13 - Overwriting tags start values and retaining them

In my program my program tags largely exist in a couple of a data blocks. There are a number of tags in there that the operator may need to get to in order to change the value, so for alarms the high and low alarm and trip levels (so that is 4 tags per channel), or for the scaling calibrations the gain and offset values.

I am struggling to get my head around ‘Start Value’, Default Value’, ‘Retain’ and ‘Setpoint’ values. I have mapped over the alarm, trip and calibration tags to the HMI and can change the values with a mapped I/O field, but when I go live I can see that these values are just held in the ‘Monitor Value’. Should the PLC go off-line then it will then go back to the default or ‘Start Values’. I guess what I’m asking is how can I have an operator with access to the HMI, permanently overwrite a tag starting value that the PLC will hold in its non-volatile memory?

as always, cheers for any pointers.

Had to look up what Set Points were myself.

Start value is whatever you want the value to be to begin with. If you reload the database in to the PLC all values will be reinitialised with their 'Start values'. Though you can get round this problem by using the Download without reinitialsation button, though I haven't tried that myself yet.

Retain is the bit you want to use to make something still hold a value after a power cycle.

Set Point can be used to reset all those variables marked as Set Points back to their Start Values by clicking on the Initialise setpoints icon.

Have a look at the buttons below for storing data.

Thanks Bryan. It's that start value that I want to change though. If I calibrate a channel and give it a gain number to change counts to an engineering unit and then give it an offset, in 6 months time I'll redo the cal and the values will be changed. After this I'm only interested in it being latest values and not the original. There must be a way of overwriting the start values from the HMai without needing to use TIA Portal and snapshot, download, etc? The operators have to be able to do this without software.

Why would you need to change the start values as values will be stored in the DB?

Only if you change the DB(change length etc) you would need to know the values, but this can be done by making a upload of the DB before changing the DB.

'Retain' is the bit you want to use to make something still hold a value after a power cycle. Set the 'Retain' marker and it will keep the current value. If you change the current value then the new value will be retained.