Siemens SIMATIC S5-115U, Руководство пользователя

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S5-115U Manual Analog Value Processing
10.7 Wirebreak Signal and Sampling for Analog Input Modules
Wirebreak Signal
Wirebreak is signalled only in the case of the 460 and 465 analog input modules.
If a 6ES5 498-1AA11 range card (through-connection card) is used, you can select the "Wirebreak
signal" function to monitor the sensors connected to the inputs (see Tables 10-1 to 10-4). You can
select wirebreak detection for 8 or 16 inputs for 16-channel operation or for 4/8 inputs for
8-channel operation.
The wirebreak signal is issued under the following conditions:
Before each input value is decoded, a constant current is applied briefly (1.6 ms) to the input
terminals and the resulting voltage compared with a limiting value. If the sensor circuit or supply
lead is interrupted, the voltage exceeds the limiting value and a wirebreak signal is generated
(bit 1 is set in data byte 1; refer to Section 10.5.1). The ADC decodes the value "0".
When the signal at the input is measured with a digital voltmeter, the constant-current pulses
may cause apparent fluctuations in the signal. When the input circuit that supplies the analog
value has capacitive characteristics, the constant current falsifies the measured value.
Should these apparent fluctuations in the signal prove annoying, e.g. on startup, the test current
can be deactivated on the 460 and 465 analog input modules by ap24 V to pin 26 in the
front connector and 0 V to pin 47 (L-) or to analog input module 465, pin 37 (M
ext
). In addition,
mode selector I must be set to "No wirebreak signal".
A wirebreak signal serves a practical purpose only in conjunction with a 6ES5 498-1AA11 through
connection card. It is not possible to detect a wirebreak on the 6ES5 498-1AA41, -1AA51 or
-1AA71 range cards, as the measuring inputs are terminated with low-resistance shunts. On all
other range cards, a wirebreak signal results in an undefined reaction.
EWA 4NEB 811 6130-02b
10-51