5.12 Defining the Units
The units parameter defines the range and/or type of data value associated with an input or output.
Selecting Units from within any configuration tool changes the units definition of several parameters, including threshold,
hysteresis, and delta. For example, if the units are 0 to 20 mA, the threshold, hysteresis, and delta values are entered as
milliampere values. Selecting Temp °C changes the threshold, hysteresis, and delta units to degrees Celsius.
Signed values range from −32768 to +32767 and allow for the measurement of negative values. Signed values are typically
used for measuring temperatures. Signed values are stored as two's complement values.
Unsigned values range from 0 to 65535 and are used to measure values that do not go below zero, such as 4 to 20 mA,
distance, or a counter.
5.12.1 Interpreting Register Values in the Banner Wireless System
The units conversion table defines the type and range of values for each type of I/O.
The wireless devices have many different units of measure for inputs including: milliamp (mA), voltage (V), temperature (°C
or °F), humidity (RH), or a raw 16-bit or 32-bit value. Outputs can be either current (4 to 20 mA, 0 to 20 mA) or voltage (0 to
10 V dc). All values stored in Modbus registers are unsigned numbers, except for temperature readings. The temperature
readings are stored as signed numbers (two's complement).
The following table defines the range of values and descriptions for input units.
Input Type
I/O Range
Holding Register
Representation
Data Conversion
Description
Min.
Max.
Min.
Max.
Discrete
0
1
0
1
-
-
0 to 20 mA
0.0 mA
20.0 mA
0
65535
(20 mA ÷ 65535) × Reg Value = mA
Linear mapping of unsigned register
value to current
4 to 20 mA
4.0 mA
20.0 mA
0
65535
((16 mA ÷ 65535) × Reg Value) + 4 =
mA
Linear mapping of unsigned register
value to current
0 to 10 V dc
0.0 V dc
10.0 V dc
0
65535
(10 V ÷ 65535) × Reg Value = V
Linear mapping of unsigned register
value to voltage
Temp C/F (high resolution) –1638.3
+1638.4
0
65535
(Converted Reg Value) ÷ 20 = Temp
Signed Values
Counter
0
65535
0
65535
-
-
16-bit T30UF
0 mm
65535 mm
0
65535
None; stored as millimeter value
Unsigned
Humidity
0% RH
100% RH
0
10000
(Reg Value) ÷ 100 = Relative Humidity
(RH)
Unsigned
Temperature Measurements:
• In high resolution mode, the temperature = (Modbus register value) ÷ 20. For high resolution temperature input, 0 in
the register is interpreted as 0° and 65535 in the register (0xFFFF) is interpreted as −1 ÷ 20 = −0.05°.
• In low resolution mode, the temperature is (Modbus register value) ÷ 2. For low resolution temperature input, 0 in the
register is interpreted as 0° and 65535 in the register (0xFFFF) is interpreted as −1 ÷ 2 = −0.5°. The I/O range values
are –16383 through 16384.
When using a 4 to 20 mA sensor with a 0 to 20 mA input, the sensor uses the 4 to 20 mA section of the total range. Using a
4 to 20 mA with a 0 to 20 mA input allows you to determine when you have an error condition with the sensor. A normal
input reading between 4 and 20 mA indicates a functioning sensor whereas a value below 4 mA indicates an error condition,
such as a broken wire or loose connection. Some Sure Cross devices allow you to configure the analog inputs and outputs
to use either 0 to 20 mA or 4 to 20 mA.
Sure Cross
®
Performance DX80 Wireless I/O Networks
www.bannerengineering.com - Tel: + 1 888 373 6767
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