Banner SureCross DX80 Wireless Networks - Manual (Page 29)

• 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 inter-
preted as 0° and 65535 in the register (0xFFFF) is interpreted as −1 ÷ 2 = −0.5°. The I/O range vlaues are –16383 through 16384.
When using a 4-20 mA sensor with a 0-20 mA input, the sensor uses the 4-20 mA section of the total range. Using a 4-20 mA with a 0-20
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 DX80 SureCross devices allow you to configure the analog inputs and outputs to use either 0-20 mA or 4-20 mA.
Signed Numbers
Temperature values are stored in Modbus registers as two's complement signed numbers. Using two's complement allows negative num-
bers to be stored in Modbus registers. Although not technically a sign bit, the most significant bit (MSB) indicates a negative number
when the value is set to one (1). When the most significant bit is zero (0), the value is greater than or equal to zero.
Modbus register values of 32768 through 65535 (decimal) represent negative temperatures. These numbers in binary form are: 1000
0000 0000 0000 through 1111 1111 1111 1111.
To convert to a negative temperature value from a Modbus register value, first convert the value from the two's complement number. To
convert from a two's complement number in binary form, invert all the bits (0 changes to 1, 1 changes to a 0), then add 1. Convert this
binary value to a decimal value and divide by either 20 (high resolution mode) or 2 (low resolution mode) to calculate the negative tem-
perature.
Register Value Converted Decimal Calculated Temperature
(Converted Decimal ÷ 20) Two's Complement Value Decimal Value
0000 0000 0000 0101 5 5 0.25
0000 0000 0000 0100 4 4 0.20
0000 0000 0000 0011 3 3 0.15
0000 0000 0000 0010 2 2 0.10
0000 0000 0000 0001 1 1 0.05
0000 0000 0000 0000 0 0 0
1111 1111 1111 1111 65535 -1 -0.05
1111 1111 1111 1110 65534 -2 -0.10
1111 1111 1111 1101 65533 -3 -0.15
1111 1111 1111 1100 65532 -4 -.20
1111 1111 1111 1011 65531 -5 -0.25
1111 1100 0001 1000 64536 -1000 -50
Mapping Unit Types
Using signed or unsigned value types allows the user to generically map any input to any output. The signed and unsigned values read
the null and span parameters to create the linear translation between one scale and another. The output type is set to mA or V.
Output = (Fullscale/Span)(InputValue − Null) + Offset
Output Scale Fullscale (range) Offset
0 to 20 mA 20 mA 0 mA
4 to 20 mA 16 mA 4 mA
SureCross User Configuration Tool (UCT)
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