11
After the device restarts, the first time synchronization should be done by sending either
a “Read” or “Clear” command. The “Write” commands sent immediately after the device
restarts will be ignored until the CANopen link is synchronized.
In order to provide reliable synchronous reads and writes in a natively asynchronous
CANopen environment, it is recommended to follow a couple of simple rules:
1.
Do not change control byte 0 in the request buffer until all other parameters
are set. This guarantees that your request will not be carried out while you
change the point address or data. Write byte 0 with your new command after
you completed setup of the remaining bytes.
2.
Do not leave your write command in the request buffer for a long time.
Remove it immediately with a “Clear” or “Read” command after you received
an acknowledgement.
16-bit Scaled Analog Data
To avoid over-range errors with 16-bit data, liner scaling may be used to scale 32-bit
analog readings to 16-bit integer format. When 16-bit data is requested by the master
and the scaling bit in the master request is set to 1, any analog register (excluding setup
data, counters and binary bit-mapped registers) will be scaled to the range of -32768 to
32767 for bi-directional parameters (such as power and power factor), and to the range
of 0 to 32767 for single-ended positive parameters (voltage, current, frequency, etc.). To
get a true reading, the reverse conversion should be done using the following formula:
Y = ((X
–
RAW_LO)
(ENG_HI
–
ENG_LO)) /(RAW_HI
–
RAW_LO) + ENG_LO
where:
Y
-
True reading in engineering units
X
-
Raw input data in the range of RAW_LO to RAW_HI
ENG_LO,
ENG_HI
-
Data low and high scales in engineering units (see Section 4 for device data
scales)
RAW_LO
-
Low conversion scale for raw device data:
RAW_LO = -32768 for a point with a negative LO scale,
RAW_LO = 0 for a point with a zero or positive LO scale
RAW_Hi
-
High conversion scale for raw device data: RAW_HI = 32767
Refer to Section 4 “Data Scales and Units” for applicable data scales and measurement
units. The default voltage scale in the device is 144V (120V+20%). It can be changed via
the supplemental PAS software. The recommended voltage scale is 120V+20% = 144V
for using with external PT’s, and 690V+20% = 828V for a direct connection to power line.
NOTE: If a source data value exceeds the device engineering scale, it is truncated to a
maximum allowable negative or positive number and the “over-range error” exception
code is returned in the response control word.
CONVERSION EXAMPLES
1. Voltage readings
a) Assume device settings (direct wiring): PT ratio = 1; Voltage scale = 828V (690V + 20%).
Voltage engineering scales (see Section 4):
ENG_HI = Vmax = 828.0
PT ratio = 828.0
1 = 828.0V
ENG_LO = 0V
If the raw data reading is 4748 then the voltage reading in engineering units will be as follows:
Volts reading = (4748 – 0)
(828.0 - 0)/(32767 - 0) + 0 = 120.0V
b) Assume device settings (wiring via PT): PT ratio = 14,400V : 120V = 120; Voltage scale = 144V.
Voltage engineering scales (see Section 4):
ENG_HI = Vmax = 144.0
PT ratio = 144
120 = 17,280V
ENG_LO = 0V
If the raw data reading is 27245 then the voltage reading in engineering units will be as follows:
