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be re start ed until RESET switch is man u al ly pressed.
LRA/FLA Po ten ti om e ter R16 is fac to ry adjusted (fi eld
ad just ed on service replacements) to the ratio of Locked
Rotor Amps to Full Load Amps. The correct setting is
determined by dividing the LRA by the FLA. If Switch
S1 is in the "Y-Delta/57%" po si tion, there is no 245%
FLA thresh old. Switch S1 must be positioned accord-
ing to the type of Electro-Me chan i cal starter present;
UP for Y-delta or Autotransformer start ers, DOWN for
Across-the-Line starters.
The Multiplexer (MUX) is an electronic switch with 8
inputs and 1 output. The address applied to it de ter mines
the position of the switch (i.e., which input is rout ed
to the output). The inputs to channel 0 through 6 are
grounded (0VDC) . The input to channel 7 is a 0 to
4.0VDC analog signal, representing motor current over
the range of 0 to 100% FLA. It is Factory calibrated by
Po ten ti om e ter R34 to be 4.0VDC when the com pres sor
motor current is at 100% FLA. Under Program con trol,
the Microboard commands the MUX to route the in puts
to the MUX output by ap ply ing 3-bit Binary ad dress es
to the MUX address inputs at J5-1,2,3. The volt age level
for a logic 1 is +12VDC and logic 0 is 0VDC. The
Microboard reads the MUX outputs at J5-6. It fi rst ad-
dress es chan nel 0 to de ter mine the type of starter applied.
The 0VDC at channel 0 indicates to the Microboard
that this is an Electro-Mechanical Starter ap pli ca tion
(In all start er ap pli ca tions, the Micro reads chan nel 0 to
determine the type starter applied; 0VDC = EM starter,
>0VDC=Solid State Starter). It then ad dress es channel
7 (ignoring chan nels 1 through 6) to read the analog
motor current volt age. The Microboard in ter prets this
analog value in terms of %FLA and dis plays it upon
operator keypad request. It also uses this value to invoke
compressor motor Current Limit at 100% FLA and
104% FLA. When mo tor current rises to 100% FLA, the
Microboard pre vents any further current rise by in hib -
it ing further Pre-ro ta tion Vanes (PRV) open ing until it
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de creas es to 98% FLA. If the motor current continues
to rise to 104% FLA, the Microboard ap plies a close
sig nal to the PRV until the motor current decreases to
102% FLA. While Current Limit is in effect, MOTOR
- HIGH CURRENT LIM IT is dis played.
As detailed in the "System Calibration" section of this
book, to fi eld calibrate Potentiometer R8, the PRV must
be manually operated to achieve 105% FLA com pres sor
motor current. Therefore, during this procedure, Cur-
rent Limit is not invoked until 107% FLA and 110%
FLA. The fi rst time the PRV OPEN key is pressed on the
COM PRES SOR Screen after logging in at SER VICE
access level, a 10 minute window is opened, al low ing
the cur rent to rise to 107% FLA be fore further PRV
opening is inhibited. This inhibit is re leased when the
current decreases to 106% FLA. If the current con tin ues
to rise to 110%, manual control is overridden and a close
signal is applied to the PRV until the current de creas es
to 109% FLA. After 10 min utes, the normal current limit
thresholds of 100% FLA and 104% FLA are ap plied.
The MUX address inputs along with respective outputs
are as follows:
BINARY
DECIMAL
J5-1 J5-2
J5-3
0
0
0
0
0
0
1
1
0
1
0
2
0
1
1
3
1
0
0
4
1
0
1
5
1
1
0
6
1
1
1
7
FORM 160.54-M1(503)
OUT PUT
Ground
Ground
Ground
Ground
Ground
Ground
Ground
0-5.0VDC mo tor cur rent
an a log sig nal cal i brat ed on
CM-2 board to be +4.0VDC at
100% FLA.
65
10
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