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Virtual sensors

Overview

Virtual sensors allow displaying value calculated using:

  • data from any sensors
  • mathematical formulas

This powerful tool can can display gauges, piecharts, textual information, etc.

Data calculated by virtual sensors can also be viewed in charts module.

Visualization

Virtual sensor widgets
Virtual sensor widgets

Limits

Basic feature set allows you to create one virtual sensor per gateway.
This limit can be upgraded to up to 20 virtual sensors per gateway.

Formulas

Writing a formula

A formula is a mathematical expression.

Example 1 - summing power

Lets say we have two energy meters: * e1 - a main incomer * e2 - photovoltaic energy generation and we would like to display how much power is our warehouse using at the moment.

To do that we need to add power from both meters. We can do it using this simple formula:

val(e1.pwr) + val(e2.pwr)

Example 2 - average temperature

Lets say we have three 1-Wire temperature sensors and we would like to find out what is the average temperature.

We can do it using this simple formula:

( val(70) + val(71) + val(72) ) / 3

Basic functions

Function Description
val(sensorId) returns value of sensor (recommended)
raw(sensorId) returns raw value of sensor (special use only)
if(x,a,b) if X then a else b
text(x,a,b) if X then a else b
fixed(x,y) display numeric value x as decimal with y digits after dot

Mathematical functions

Function Description
sin(x) Sine of x (x is in radians)
cos(x) Cosine of x (x is in radians)
tan(x) Tangent of x (x is… well, you know)
asin(x) Arc sine of x (in radians)
acos(x) Arc cosine of x (in radians)
atan(x) Arc tangent of x (in radians)
sqrt(x) Square root of x. Result is NaN (Not a Number) if x is
log(x) Natural logarithm of x (not base-10).
abs(x) Absolute value (magnatude) of x
ceil(x) Ceiling of x — the smallest integer that’s >= x.
floor(x) Floor of x — the largest integer that’s <= x
round(x) X, rounded to the nearest integer.
exp(x) ex (exponential/antilogarithm function with base e)

Aditional functions

Function Description
random(n) Get a random number in the range [0, n). If n is zero, or not provided, it defaults to 1.
fac(n) n! (factorial of n: “n * (n-1) * (n-2) * … * 2 * 1″)
min(a,b,…) Get the smallest (“minimum”) number in the list
max(a,b,…) Get the largest (“maximum”) number in the list
pyt(a, b) Pythagorean function, i.e. the c in “c2 = a2 + b2“
pow(x, y) xy. This is exactly the same as “x^y”.
atan2(y, x) arc tangent of x/y. i.e. the angle between (0, 0) and (x, y) in radians.