67
5.2.20
Virtual Input – Calculation
A Calculation type Virtual Input is not a physical sensor; it is a value that is calculated from two physical sensor
inputs. The analog values that can be used for each type of calculation are selected from a List of all defined sensor
inputs, analog inputs, flowmeter rates, the other virtual input, solid state relay %, and analog output %.
Calculation modes are:
•
Difference
(Input - Input 2)
•
Ratio
(Input / Input 2)
• This selection could be used to calculate Cycles of Concentration in HVAC applications, for example
•
Total
(Input + Input 2)
•
% Difference
[(Input - Input 2) / Input]
• This selection could be used to calculate % Rejection in RO applications, for example
Virtual Input Details
The details for any type of virtual input include the current value calculated, alarms, the status, and the input type.
Settings
Touch the Edit icon to view or change the settings related to the virtual input.
Alarms
Low-Low, Low, High and High-High Alarms limits may be set.
Deadband
This is the Alarm Deadband. For example, if the High Alarm is 7.00, and the deadband
is 0.1, the alarm will activate at 7.01 and deactivate at 6.90.
Input
Select the physical input or select Constant, whose value will be used in the calculation
shown above as the Input in the formula.
Constant
Only appears if the Input selection is Constant. Enter the value.
Input 2
Select the physical input or select Constant, whose value will be used in the calculation
shown above as the Input 2 in the formula.
Constant 2
Only appears if the Input 2 selection is Constant. Enter the value.
Calculation Mode
Select a calculation mode from the list.
Alarm & Datalog
Suppression
If any of the relays or digital inputs are selected, any alarms related to this input
will be suppressed if the selected relay or digital input is active. At the same time,
all datalogs and graphs containing the input will show no data for the duration of
the activation.
Low Range
Set the low end of the normal range for the calculated value. A value below this will
trigger a Range Alarm and deactivate any control output using the virtual input.
High Range
Set the high end of the normal range for the calculated value. A value above this will
trigger a Range Alarm and deactivate any control output using the virtual input.
Smoothing Factor
Increase the smoothing factor percentage to dampen the response to changes. For ex-
ample, with a 10% smoothing factor, the next reading shown will consist of an average
of 10% of the previous value and 90% of the current value.
Name
The name used to identify the input may be changed.
Type
Select the type of input; either Calculation, Redundant, Raw Value, Disturbance,
or Not Used.
5.2.21
Virtual Input – Redundant
A Redundant type Virtual Input is not a physical sensor; it is a value that is calculated from two physical sensor
inputs. The redundant sensor algorithm compares the readings from two sensors, and chooses which sensor to use.
The value of the virtual input is the value of the sensor chosen by this comparison.
If the difference between the two exceeds a programmable amount, a deviation alarm is set, but control continues.
If one of the sensors goes into a range error or a fault alarm, the other sensor will take over. If both sensors give
