Xylem XL Series H-522 - Plus - Manual (Page 208)

18-2 4 To 20 Milliamp Output
XL™ Series
wiring and voltage levels to verify they are ok. If the current meter reads zero milliamps then the
wires could be connected backwards or there is no power source for the loop. Remember that
this output controls the current in the loop but does not provide the power for the loop. An
external power source is required.
If the current displayed on a meter is in the range of 4 to 20 milliamps but is less than what is
displayed by this option, then it may be the external power source is not big enough. In most
cases a 12 volt battery will not be sufficient to power the loop. In most cases a 24 volt battery is
required. This reading and the actual current value may track at lower values but as the current
approaches the 20.0 milliamp level the actual current as displayed on an external meter will start
to drop off indicating the battery voltage is too low.
PC Interface View Built In Display Screen
S - Data Source: None 4-20 Source [None ]
This selects what sensor is to be simulated as a 4 to 20 milliamp sensor. For example, if a
temperature sensor was connected to analog channel 1, then analog channel 1 would be set as the
data source.
PC Interface View Built In Display Screen
H - Maximum Level: 20.00 Max Value [20.00 ]
This is the maximum value to look for from the data source. Continuing on from the example
above, if the temperature probe had a range of -50 to +50 degrees, then the max level would be
set to +50, and the min level set to -50. Now a temperature of -50 would cause a milliamp output
of 4.00 milliamps and +50 degrees would produce a 20.0 milliamp output.
PC Interface View Built In Display Screen
M - Minimum Level: 4.00 Min Value [4.00 ]
This option is used to set the minimum value to look for from the data source. Use the example
from above for details on how the minimum level is used in determining the current in the loop.
Note that as the range is enlarged the resolution of the output current is decreased, and the
opposite if the range is reduced. The resolution is calculated as:
(mA Output Range) / (Input Range) = mA per Input Unit Change.