Analog modules
9.3 SM 336; F-AI 6 x 0/4 ... 20 mA HART
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
223
Wire-break check in the range of 0 to 20 mA
In the range 0 to 20 mA, a wire-break check is always performed:
●
Wire break at < 0.4442 mA with 7FFF
H
in
S7 F/FH Systems is reported and the fail-safe
value will be output as configured at the input SUBS_V of the F channel driver. In
S7
Distributed Safety, the fail-safe value 0 is provided in the PII for the safety program in
place of 7FFF
H
.
Wire-break check and underflow check in the range 4 to 20 mA
In the range 4 to 20 mA, a check is made to determine whether wire-break check is
assigned.
●
If wire-break check is assigned, an underflow check is not performed. Wire break at < 3,6
mA with 7FFF
H
in
S7 F/FH Systems is reported and the fail-safe value will be output as
configured at the input SUBS_V of the F channel driver. In
S7 Distributed Safety, the fail-
safe value 0 is provided in the PII for the safety program in place of 7FFF
H
.
●
If no wire break is assigned, in case of an underflow at < 0.4444 mA with 8000
H
in
S7 F/FH Systems is reported and the fail-safe value will be output as configured at the
input SUBS_V of the F channel driver. In
S7 Distributed Safety, the fail-safe value 0 is
provided in the PII for the safety program in place of 8000
H
(for underflow).
Measured value resolution
SM 336; F-AI 6 x 0/4 ... 20 mA HART has a 15-bit resolution.
Table 9- 14 Representation of the bit pattern
Bit number
15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
Bit significance
Sig
n
2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Example
0
1
0
0
1
1
0
0
1
1
1
1
1
1
0
1
Table 9- 15 Resolution
Measuring range
% of nominal range
Resolution
0 to 20 mA
0,0036
723.4 nA
4 to 20 mA
0,0036
578.7 nA
