F
3-
-0
8T
H
M
--n
8C
h.
T
he
rm
oc
ou
pl
e
In
.
9--8
F3--08THM--n 8-Channel Thermocouple Input
The most significant bit is used to note
the sign of the temperature. If this bit is
on, then the temperature is negative. If
the bit is off, then the temperature is
positive.
R011
MSB
LSB
1
1
0
1
1
7
1
1
6
1
1
5
1
1
4
1
1
3
1
1
2
1
1
1
-- temperature sign
The first twelve bits represent the
temperature. If you have selected the
0--4095 scale, the following format is
used.
Bit
Value
Bit
Value
0 (LSB)
1
6
64
1
2
7
128
2
4
8
256
3
8
9
512
4
16
10
1024
5
32
11
2048
1
1
7
R001
MSB
LSB
0
1
0
1
1
6
1
1
5
1
1
4
1
1
3
1
1
2
1
1
1
1
1
0
0
1
7
0
1
6
0
1
5
0
1
4
0
1
3
0
1
2
0
1
1
-- data bits
R011
Typically, the F3--08THM--n resolution enables you to detect a 1
_
C change in
temperature. The National Bureau of Standards publishes conversion tables that
show how each temperature corresponds to an equivalent signal level.
Since the module has 12-bit resolution,
the analog signal is converted into 4096
“pieces” ranging from 0 -- 4095 (2
12
). For
example, with a --2 (100mV) module a
signal of 0 mV would be 0, and a signal of
100 mV would be 4095. This is
equivalent to a a binary value of 0000
0000 0000 to 1111 1111 1111, or 000 to
FFF hexadecimal. The diagram shows
how this relates to the example signal
range.
Each “piece” can also be expressed in
terms of the signal level by using the
equation shown. The following table
shows the smallest signal levels that will
result in a change in the data value for
each signal range.
100mV
0 mV
0
4095
0--100 mV Scale
Resolution
=
H
-
L
4095
H = high limit of the signal range
L = low limit of the signal range
Range
Highest Signal
Lowest Signal
Smallest Change
0 -- 50 mV
50 mV
0 mV
12.2
µ
V
0 -- 100 mV
100mA
0mA
24.2
µ
V
Now that you understand how the module and CPU work together to gather and
store the information, you’re ready to write the control program.
Temperature Sign
Bit
Analog Data Bits
Temperature Input
Resolution
Millivolt Input
Resolution
