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UNIT OPERATION
EMS-PWM REMOTE TEMPERATURE RESET
EMS-PWM Remote Temperature Reset is a value
that resets the chilled liquid setpoint based on a PWM
input (timed contact closure) to the I/O Board. This
PWM input would typically be sup plied by an Energy
Management System.
A contact closure on the PWM Temp Reset input at
CTB1 terminals 13 and 20, will reset the chilled liquid
setpoint based on the length of time the contacts remain
closed. The maximum temperature reset is achieved
at a contact closure of 11 seconds. This is the longest
contact closure time allowed. One second is the shortest
time allowed and causes the chilled liquid setpoint to
revert back to the local programmed value. The reset
value is always added to the chilled liquid setpoint,
meaning that this function never lowers the chilled
liquid setpoint below the locally programmed value, it
can only reset to a higher value. The I/O Board must
be refreshed between 30 seconds and 30 minutes. Any
contact closure occurring sooner than 30 seconds will
be ignored. If more than 30 minutes elapse before the
next contact closure, the setpoint will revert back to
the locally programmed value. The new chilled liquid
setpoint is calculated by the following equations:
setpoint = local chilled liquid setpoint + °reset
°reset = (Contact Closure - 1) x (*Max. Reset Value)
Example:
Local chilled liquid setpoint = 45°F (7.22°C).
*Max Reset Value = 10°F (5.56°C)
Contact Closure Time = 6 Seconds.
(English)
(6 sec. - 1) (10°F/10) = 5°F Reset
So, the new chilled liquid setpoint = 45°F + 5°F= 50°F.
This can be viewed by pressing the COOLING SET-
POINTS key twice. The new value will be dis played as
"REM SETP = 50.0°F."
(Metric)
(6 sec - 1) * (5.56°C/10) = 2.78°C
Reset Cooling Setpoint = 7.22°C + 2.78°C = 10.0°C
So, the new reset Cooling Setpoint = 7.22 °C + 2.78°C
= 10°C. This can be viewed by pressing the COOLING
SETPOINTS key twice. The new value will be displayed
as "REM SETP = 10.0°C."
*
Max Reset Value is the "Max EMS-PWM Remote Temp. Reset" setpoint value described in the "Setpoints Keys" segment of
Section 2 in this IOM. Programmable values are from 2°F to 40°F (1.11°C to 22.2°C).
124
BAS/EMS TEMPERATURE RESET OPTION
The Remote Reset option allows the control center
of the unit to reset the chilled liquid setpoint using a
0 to10VDC input, a 4 to 20mA input, or a contact
closure input. The Remote Reset circuit board
converts the signals mentioned above into pulse width
modulated (PWM) signals which the microprocessor can
understand. Whenever a reset is called for, the change
may be noted by pressing the COOLING SETPOINTS
key twice. The new value will be displayed as "REM
SETP = XXX°F."
The optional Remote Reset option would be used when
reset of the chilled liquid setpoint is required and a
PWM signal (timed contact closure) cannot be supplied
by an Energy Management System. The Remote Temp.
Reset Board will convert a voltage, current, or contact
signal that is available from an EMS to a PWM signal,
and every 80 seconds provide a PWM input to the I/O
Board. Figure 12 shows a diagram of the field and
factory electrical connections.
If a 0 - 10VDC signal is available, it is applied to
terminals A+ and A-, and jumpers are applied to JU4 and
JU2 on the reset board. This DC signal is conditioned
to a 1 to 11 second PWM output and supplied to the
PWM input on the I/O Board at CTB1 terminals
10
13 and 20. To calculate the reset chilled liquid setpoint
for values between 0VDC and 10VDC use the following
formula:
setpoint = local chilled liquid setpoint + °reset
°reset = (DC voltage signal) x (*Max Reset Value)
Example:
Local chilled liquid setpoint = 45°F (7.22°C)
*Max Reset Value = 20°F (11.11°C)
Input Signal = 6VDC
(English)
°reset = 6VDC x 20°F = 12°F reset
setpoint = 45°F + 12°F = 57°F
(Metric)
°reset = 6VDC x 11. 11°C = 6.67°C reset
setpoint = 7.22°C + 6.67°C = 13.89°C
FORM 150.62-NM8 (1020)
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JOHNSON CONTROLS
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Troubleshooting
