Siemens SIMATIC S5-90U System Manual page 418

Module Spectrum
Start-Up of the Module
Set the intended operating mode using the switch on the front panel of analog input module 464-
8MA21. This switch is located on the right side at the top of the front panel of the module.
Power supply Set the switch to the available power supply frequency. This selects the inte-
frequency: gration time of the A/D converters for optimal interference voltage suppression.
Power frequency 50 Hz:
Power frequency 60 Hz:
Operation: Set the number of channels you wish to assign on the analog input module. If
there are fewer than four channels, the measured values will be updated faster.
Broken wire: Once the broken wire signal has been activated, a break on one of the lines to
the sensor (thermocouple) or of the sensor itself causes the red LED above the
function selection switch to light up. At the same time, the broken wire error bit
F (bit 1, byte 1) for the faulty channel is set.
The module "recognizes" a wire break by applying a conventional tripping
current to the input terminals and by comparing the resulting voltage to a limit
value. If there is a wire break in the sensor or the lines, the voltage exceeds
the limit value and a "wire break" signal is sent. When the signal at the input is
measured with a digital voltmeter, the tripping current pulses cause apparent
fluctuations of the signal. Deactivation of the wire break signal does not turn off
the tripping current.
Linearization: With this function, you can obtain a characteristic linearization of the thermo-
couples of type J, K, and L.
With module 464-8MA21, the linearization must always be activated together
with the corresponding compensation of the reference point temperature.
Thermocouples:
Type J: - 200° C (-328° F) to
Type K: - 200° C (-328° F) to
Type L: - 199° C (-326° F) to
Temperature
compensation: For the thermocouples of type J, K, and L, you can compensate, on the one
hand, the temperature of the reference point using an external compensating
box.
On the other hand, it is possible to move the reference point to the front of the
module by activating the "temperature compensation" function. When thermo-
couples are directly connected, an internal circuit on the module causes the
digital value "0" to be displayed independently of the temperature of the
terminal when the temperature at the measuring junction is 0° C (32° F). In
order to accomplish this, the terminals of the sensors have to be connected
directly or via an equalizing conductor to the module, i.e., without a copper
extension cable (see Figures 15-5, 15-6).
15-52
Integration time 20 ms
Integration time 16.66 ms
+1200° C (1392° F)
+1369° C (2497° F)
+900° C (1652° F)
S5-90U/S5-95U
(in steps each of 1° C
(1.8° F)).
EWA 4NEB 812 6115-02b