Within the configuration of an ezeio, mathematical expressions are used to produce a value/result for “Fields”, “Alarms” and “Conditions”. This powerful tool can produce mathematical and logical results using multiple constants and/or variables from the available resources on an ezeio. Expressions can be as simple as the constant “1” to indicate True/ON or as complex as necessary.

Many of the valid functions and operators will be familiar to you, such as +, -, >, <, and =. Others come from advanced mathematics and logic, such as sin(), tan(), ||, and &&. Another category relates specifically to eze System terms and functions, such as Day() and K2F().

The syntax structure of eze System expressions follows common mathematical and logic standards for precedence and functional format.

For example, 2+3*4 equals 2+(3*4) or 14, since multiplication takes precedence over addition.

Any value greater than 0 is considered 'true'.

0 and all negative values are considered 'false'.

The result of a condition, such as (f(1)>45), results in the value 0 (if false) or 1 (true).

The Data Expression box under Field configuration determines the value of the field.

If left blank, the field value is not updated by the system, and will simply remain the same until changed by the user manually or by a script using the SetField function.

The most common field expression simply takes the value of a register and applies it to the field.

r(4, 2)   // get the value from device #4, register 2

A single expression can reference other fields and registers.

f(4) + f(5)         // the sum of the values in field #4 and field #5
r(1,1) * 100 - 50   // multiply the value of register 1 on device 1 with 100 and subtract 50
abs(f(10)-f(12))    // the absolute difference between field 10 and 12

The Data Expression is evaluated at a fixed rate of 10 times per second (100ms interval). This can be used to create counters and accumulators.

If our Field #1 monitors the current draw of a device, and the device is considered running if the current exceeds 5A, we can use this expression to count the total run-time in seconds in field #2:

Field #2 Data expression:

f(2) + ( f(1)>5 )/10

Starting with the condition (f(1)>5), this will return 0 (false) if the device is not running, and 1 (true) if it is running. So as long as the device is not running, we're adding zero to the f(2) counter. When the device is running we are adding 0.1 to the f(2) counter, and since this happens 10 times per second, we'll add a total of 1 each second.

This way we've implemented a run-time counter.

Assume our Field #1 holds the output of a flow sensor, in L/s (Liters per second).

We want out Field #2 to reflect the total amount in Liters.

Field #2 Data expression:

f(2) + f(1)/10

We simply add 1/10th of the value of the momentary flow to our accumulator f(2).

In this example, field 1 holds our momentary power in kW. We want to accumulate this into energy (kWh) over time.

Field #2 Data expression:

f(2) + f(1)/36000

Since we are looking for kW-hours, we need to divide the momentary power with 36000 (3600 seconds in an hour, and we are re-evaluating 10 times per second).