Spectrum 1734, Руководство пользователя

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Chapter 4: OE2CIH and HART 4-11
User’s Manual Pub. 0300272-03 Rev. B
clamping is enabled (see below).
The Program Value is clipped to the range limits as follows:
•
0 to 20 mA: 0.0 mA to 21.0 mA
•
4 to 20 mA: 3.0 mA to 21.0 mA
When both Fault and Program conditions exists simultaneously, the Fault
condition takes priority.
High/Low Engineering Values (User Scaling)
High/Low Engineering Values are signed 16-bit integers. Values may range from
32767 to -32768. These values are to determine the scaling of Output Words to
actual current for each channel:
•
For 0 to 20 mA range, the Low Engineering Value represents 0 mA;
High Engineering Value represents 20 mA.
•
For 4 to 20 mA range, the Low Engineering Value represents 4 mA;
High Engineering Value represents 20 mA.
It is considered a configuration error if the values are equal. Negative scaling is
also not allowed which means the High Value must always be greater than the
Low Value.
The scaling formula is as follows:
output_mA = user * gain + offset
Where:
•
output_mA = The current present at the terminal block in Milliamps
•
user = The user value in the channels Output Word
•
gain = (range_high–range_low)/(user_high–user_low)
-
range_high = (20.0 for both range settings).
-
range_low = (0.0 = 0 to 20 mA range; 4.0 = 4 to 20 mA range)
-
user_high = (user-defined INT): Constrained by the above
limitations
-
user_low = (user-defined INT): Constrained by the above
limitations
•
offset = range_low–(gain*user_low)
Examples:
•
Range = 4 to 20 mA
-
High Value = 20000
-
Low Value = 4000
For an output value of 10000, the channel shall drive 10 mA.
It is possible to enter a value of 30000, which scales well beyond the capabilities
of this module. In this case, the output will be set to either the High Limit value
(see below) or drive to its maximum capabilities.
To achieve the highest output resolution, it is necessary to use the full 16-bit
range for the endpoints.
•
Range = 0 to 20 mA or 4 to 20 mA
-
High Value = 32767
-
Low Value = -32768
It is also possible to configure scaling to allow the full output limit.