Comparison
64
Comparison
(Thermostat/differential function)
Simple description of the function:
Two values, Va and Vb + differential, are compared to produce the two output variables Va > Vb and
Va < Vb.
Input
variables:
Output
variables:
Enable comparison
Status Va > Vb + diff = Value a is greater than
value b
Comparative Value a
= First comparison value Status Va < Vb + diff = Value a is lower as
value b, indication of the output
Comparative Value b = Second comparison
value
Special features:
Only one sensor input / one output variable for another function is admissible for the value a.
Value b can also be a flexible (temperature) value. If so,
User
has to be indicated as the
"
source
." The user can see the value b as a common function parameter when it appears in
the menu of the function.
Generally this function applies to a thermostat. Use the "
function variable
" (FUNC.VAR.) to
make comparisons of any figures. Possible selections: temperature, dimensionless, flow rate,
output, heat amKWh, heat amMWh, number of impulses, time, solar radiation, relative humidi-
ty, wind speed and pressure.
The comparison difference consists in the differential between the switch-on and switch-off.
Both Va > Vb and Va < Vb can be used as output variables. When comparing a temperature
sensor with a threshold value (value b is entered as "user" under the input variables), this ba-
sically functions as a mechanical thermostat with mutual contact (Va > Vb = make contact and
Va < Vb = break contact).
If sensors have been assigned to both values, the result is a simple differential function.
If enable is set to "OFF", then
both
output variables are set to "OFF".
Entire menu view:
DES: COMP.1
FUNCTION STATUS:
INPUT VARIABLE:
OUTPUT VARIABLE:
FUNC.VAR: Temp.
Comparison of two temperatures
VALUEa: 39.1 °C
VALUEb: 44.3 °C
DIFF.ON: 5.0 K
Switch on if value a exceeds 49.3°C (44.3 + 5.0)
DIFF.OFF: 2.0 K
Switch on if value a falls below 46.3°C (44.3 + 2.0)
WARNING:
The output status of the second output variable is the inverse of the first output variable
Va > Vb + diff. The designation Va < Vb + diff for the second output variable is thus inaccurate. This
representation was selected because the display cannot indicate the inverse symbol.
If to sensors are compared, the connection of the warmer sensor (generator) to Va is recommended.
If the link between values a and b are adversely linked in the input variables, switching will then be
based on a negative differential.
