Siemens S7-300 - Page 183

Analog modules
9.2 SM 336; AI 6 x 13 Bit
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
183
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. In
S7 F/FH
Systems
, wire break is reported with 7FFF
H
if the current is < 3.6 mA. In S7 Distributed
Safety
, the fail-safe value 0 is provided in the PII for the safety program in place of
7FFF
H
.
● In
S7 F/FH Systems , if wire-break check is not configured, underflow is reported with
8000
H
if the current is < 1.18 mA. 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
The SM 336; AI 6 x 13Bit has a 13-bit resolution. That is, the last two bits are set to zero.
The values returned must be multiples of four. 1 digit (13-bit measuring range) corresponds
to 4 digits Simatic.
Table 9- 2 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 0
Table 9- 3 Resolution
Measuring range % of nominal range Resolution
0 mA to 20 mA 0,014 2.89 μA
4 mA to 20 mA 0,014 2.32 μA
0 V to 10 V 0,014 1.45 mV
WARNING
Only the measuring range 4 to 20 mA is allowed when operating in safety mode.