X20 system modules • Analog input modules • X20AI4622
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X20 system User's Manual 3.10
4.3.11.8.8 Limit values
The input signal is monitored at the upper and lower limit values. These must be defined according to the operating
mode:
Limit value (default)
Voltage signal ±10 V
Current signal 0 to 20 mA
Current signal 4 to 20 mA
Upper maximum limit value
+10 V
+32767 (0x7FFF)
20 mA
+32767 (0x7FFF)
20 mA
+32767 (0x7FFF)
Lower minimum limit value
-10 V
-32767 (0x8001)
0 mA
0
1)
4 mA
0
2)
1)
The analog value is limited down to 0.
2)
The analog value is limited down to 0 at currents <4 mA. The status bit for the lower limit is set.
Other limit values can be defined if necessary. Limit values are valid for all channels and activated automatically
by writing to the limit value registers. From this point on, the analog values will be monitored and limited according
to the new limits. The results of monitoring are displayed in the status register.
Examples of limit value settings
Application case
Limit value settings
Current signal: 4 to 20 mA
A negative limit value must be configured in order to measure values <4 mA with a current signal of 4 to
20 mA: 0 mA is equal to a value of -8192 (0xE000).
Mixed voltage and current signal
The configured limit values are valid for all channels. Mixed operation (voltage and current signal) there-
fore requires a compromise.
The following configuration has proven effective:
Upper limit = +32767, lower limit = -32767
This makes it possible to also measure negative voltage values. A lower limit value of 0 would limit the
voltage value to 0.
Current signal on all channels
All channels are configured for measuring current. The limit value setting in Automation Studio is not
adjusted automatically. That means that +32767 is configured as the upper limit value and -32767 as the
lower limit value. The necessary changes must be made by the user, e.g. lower limit value = 0
4.3.11.8.8.1 Lower limit value
Name:
ConfigOutput03
This register can be used to configure the lower limit for analog values. If the analog value goes below the limit
value, it is frozen at this value and the corresponding error status bit is set.
Data type
Value
INT
-32,768 to 32,767
Information:
•
The default value of -32768 corresponds to the minimum default value of -10 VDC.
•
When configured as 0 to 20 mA, this value should be set to 0.
•
When configured as 4 to 20 mA, this value can be set to -8192 (corresponds to 0 mA) in order
to display values <4 mA.
Information:
Keep in mind that this setting applies to all channels!
4.3.11.8.8.2 Upper limit value
Name:
ConfigOutput04
This register can be used to configure the upper limit for analog values. If the analog value goes above the limit
value, it is frozen at this value and the corresponding error status bit is set.
Data type
Value
INT
-32,768 to 32,767
Information:
The default value of 32767 corresponds to the maximum default value of 20 mA or +10 VDC.
Information:
Keep in mind that this setting applies to all channels!
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