Input Type
I/O Range
Holding Register
Representation
Data Conversion
Description
Min.
Max.
Min.
Max.
0–20 mA
0.0 mA
20.0 mA
0
65535
(20 mA ÷ 65535) × Reg
Value = mA
Linear mapping of un-
signed register value to
current
4–20 mA
4.0 mA
20.0 mA
0
65535
((16 mA ÷ 65535) × Reg
Value) + 4 = mA
Linear mapping of un-
signed register value to
current
0–10V dc
0.0V dc
10.0V dc
0
65535
(10V ÷ 65535) × Reg Val-
ue = V
Linear mapping of un-
signed register value to
voltage
Temp C/F (high res-
olution)
–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 = Rela-
tive 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 4–20 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 SureCross devices allow you to configure the analog inputs and outputs
to use either 0–20 mA or 4–20 mA.
5.9.1 Signed Numbers
Temperature values are stored in Modbus registers as two's complement signed numbers. Using two's complement allows
negative numbers to be stored in Modbus registers. Although not technically a sign bit, the most significant bit (MSB) indi-
cates 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 comple-
ment 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 temperature.
Register Value
Converted Decimal
Calculated Temperature
(Converted Decimal ÷ 20)
Two's Complement Val-
ue
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
SureCross DX80 and Performance DX80 Product Manual
50
www.bannerengineering.com - tel: 763-544-3164
Rev. J