Table of Contents
DIFF() Function
The DIFF() function can be used in a variety of ways to get the difference (end-start) between a value at two timestamps. This is typically used for incrementing counters such as kWh or total liters.
Usage:
DIFF(variable, options, [days],[minutes],[min],[max]) - see below for description.
Parameters:
variable - Variable name to use
options - Type of diff (see below)
days - optional number of days to lookup before selected day
mins - optional number of minutes to offset by
min - minimum value, will result in 0 if it is below this value
max - maximum value, will result in 0 if it is above this value
Generic Variables (per device type)
DIFF('INC1_AE', 5)
Get the difference for the selected period
Device - Specific Variables
For device specific variables use a . to separate the device name:
VALUE('My Device.My Value',1)
Get the difference between current value and start of today for the variable 'My Value' in the device 'My Device'
Option Parameters
The second parameter, [options] is a number and can be any of the following
| 0 | latest value (Default) |
| 1 | DAY - Difference between start of day and latest value |
| 2 | WEEK - Difference between start of week and latest value |
| 3 | MONTH - Difference between start of month and latest value |
| 4 | YEAR - Difference between start of year and latest value |
| 5 | PERIOD - Difference between start and end of selected date range |
| 6 | AT_START_DATE - value at the start of the selected date range |
| 7 | AT_END_DATE - value at the end of the selected date range |
| 8 | PERIOD_CUMULATIVE - value between start of period and range element (in a graph) |
| 9 | FULL_MONTH - Difference between 1st and last day of month for selected date |
The third parameter is an optional one and lets you specify a number days. This is subtracted from the currently selected period to allow you to graph historic data alongside current data.
Example
Show a cumulative value for data within a period:
(DIFF('delta0_kwh',8)
The graph for cumulative values since period start looks like this:
(DIFF('delta0_kwh',5)
The graph for period for the same variable looks like this:
Get the solar generation for one year ago (365 days):
(DIFF('inverter1_AC_Total_kWh',0,365)