Siemens S5-135U/155U - Manual (Page 436)

9-54
System Manual
C79000-G8576-C199-06
9.5.3 Special Features of the 465 Analog Input Module
The 465 analog input module executes integrating processing of the digital
input signals; periodic system interference is thus suppressed.
You can adapt the process signals, according to the application, to the input
level of the analog-to-digital converter of the module with plug-in range
cards (resistor dividers or shunt resistors).
To monitor the sensors connected to the inputs, you can use the
6ES5 498-1AA11 range card (through-connection card) to implement the
“broken wire detection” mode. You can activate broken wire detection for 8
or 16 inputs in 16-channel operation, and for 4 or 8 inputs in 8-channel
operation.
Each time the input value is about to be encoded, a constant current is briefly
(1.6 ms) switched to the input terminals and the resultant current is checked
for a limit value. If a digital voltmeter is used to measure the signal at the
input, these current pulses may appear to indicate fluctuation of the signal.
The encoded value, however, is not affected.
If these apparent fluctuations of the signal are disturbing, e.g. during startup,
you can switch the tripping current to the inactive state on the 465 analog
input modules: apply + 24 V to pin 24 of the front connector, and 0 V to L-.
You must additionally set the mode switch to “without broken wire
detection.”
In the event of open-circuit of the sensor or its line, the voltage exceeds the
limit and a broken wire is indicated (bit 1 in data byte 1). The
analog-to-digital converter encodes the value 0.
A broken wire signal is only useful when the 6ES5 498-1AA11
through-connection card is used. With all other measurement cards, a broken
wire signal will result in incorrect reactions. Further details relating to the
broken wire signal can be found in Section 9.5.10.
If the measuring range is exceeded, the overflow bit (bit 2 0 of the low byte)
is set.
You have a choice of the cyclic sampling and selective sampling modes.
In the cyclic sampling mode, the module continuously encodes all measured
values. The digitized measured values are stored under the channel-related
address on the module (the high byte under this address, and the low byte
under the next higher address). The measured values can then be read by the
module at any time without waiting. When you operate the module in this
mode, you can set a module address from 0 to 255.
Broken Wire
Signal
Switching the
Tripping Current to
the Inactive State
Measuring Range
Exceeded
Cyclic Sampling/
Selective Sampling
Analog Input/Output Modules