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6
Simplty wire 2 4-20mA devices into IN1 and IN2, in pro-
gramming step #4 select "YES", step # 5 select whether
you would like to pass the "LOW" or the "HIGH" of the
2 4-20mA signal that are wired. Either the highest or to
lowest shall be passed directly to the AO1. Step # 6 in
the programming screens allows yo to rescale the IN's
for 4-20mA to 0-20mA be selecting "0-20mA". See con-
version chart below.
dEW PoINT CoNTRoL
The analog output and digital outputs on the SZ1143b
can be setup to use a calculated dew point temperature
as the actual input. This is done by selecting "YES" in
programming step # 7. When using dew point control,
AI1 is the temperature input (automatically scaled for 0
to 100 °F) and AI2 is the relative humidity input (auto-
matically scaled for 0 to 100 %RH). In programming
screen #19, you are asked to enter a primary setpoint
which is the dew point setpoint. This setpoint will typical-
ly be the temperature of the area where condensation
is a potential problem , (i.e. cooler temperature, freezer
temperature, supply air temperature). The analog and
digital outputs behave as they normally would but use
the calculated dew point, the primary setpoint, and their
programmed parameters (heat/cool, proportional band
offsets, differentials, etc.).
Example: Door Heater Control in a Convenience Store.
The temperature inside the store is 76°F with 49% rela-
tive humidity. The coolers are kept at 37°F (entered as
the setpoint in programming screen #19).
The calculated dew point comes out to be 55°F, so:
DO1 will be OPEN (if factory defaults are used and
stage 1 is set to HEAT).
DO2 will be CLOSED (if factory defaults are used and
stage 2 is set to COOL).
AO1 will modulate based on the setpoint of 37°F, an
input of 55°F, the deadband
(programming screens #14 and #15), and the settings
chosen in programming screens #22 through #31.
AI2 ModE / PARAMETERS
Analog input two can be selected as either "Monitor",
"Remote Setpoint" or "Reset".
If monitor is chosen, the analog output and digital out-
puts are controlled based on a comparison between the
scaled AI1 value and the setpoint entered in program-
ming step #19.
If remote setpoint is chosen, the analog output and
digital outputs are controlled based on a comparison
between the scaled AI1 value, and the "setpoint" or
"scaled AI2 value".
If reset is chosen, the analog output and digital outputs
are controlled based on a comparison between AI1 and
a calculated setpoint derived from the scaled AI2 value,
the reset setpoint entered in programming step #17 and
the reset factor entered in programming step #18.
RESET
The analog output and digital outputs on the SZ1143b
can be setup to use a reset function. This is done by
selecting "Reset" in programming step # 16. When
using the reset function, AI1 is the "Primary" input and
AI2 is the "Reset" input.
In programming screen #19, you are asked to enter a
primary setpoint. This setpoint will be adjusted up and
down based on the AI2 value, the reset setpoint and the
reset factor. AI1 will be controlled to this calculated set-
point by modulating the device connected to the analog
output.
In programming screen #20, you are asked to enter a
reset setpoint. A comparison between AI2 and this set-
ting will be used in determining the calculated setpoint
for AI1.
In programming screen #21, you are asked to enter a
reset ratio factor. This is the number of units that the
AI1 setpoint is raised when the AI2 value falls below the
reset setpoint by 1 unit, or the number of units that the
AI1 setpoint is lowered when the AI2 value rises above
the reset setpoint by 1 unit.
Example: A hot water valve is controlled using an out-
4-20mA
0-20mA
4-20mA
0-20mA
4-20mA
0-20mA
4-20mA
0-20mA
4-20mA
0-20mA
4.00
0.00
8.00
5.00
12.00
10.00
16.00
15.00
20.00
20.00
5.00
1.25
9.00
6.25
13.00
11.25
17.00
16.25
6.00
2.50
10.00
7.50
14.00
12.50
18.00
17.50
7.00
3.75
11.00
8.75
15.00
13.75
19.00
18.75
