Omron PRT1-COM Operation Manual page 120

Analog Input Units
Averaging Function
Setting
Open-circuit Detection
Function
Common Power Supply
for Input Devices
Power
supply
110
The averaging function can be enabled for all inputs (0 through 3) by turning ON
pin 7 of the DIP switch. The averaging function outputs the average (a moving
average) of the last eight input values as the converted value. Use this function
to smooth inputs that vary like the one in the following diagram.
Note The time required for refreshing converted data remains one ms/point when the
averaging function is enabled. The first communications data after the power is
turned ON will be output after averaging eight samples.
The open-circuit detection function is activated when the input range is set to 1 to
5 V and the voltage drops below 0.6 V, or when the input range is set to 4 to
20 mA and the current drops below 2.4 mA. When the open-circuit detection
function is activated, the converted data will be set to 7FFF.
The open-circuit detection function is enabled or cleared when data is
converted. If the input returns to the convertible range, the open-circuit detection
is cleared automatically and the output returns to the normal range.
If an open-circuit occurs when more than one input device is using the same
power supply, and voltage input is being supplied, the following situation will
occur (this does not apply when current input is being supplied).
Input
device
Input
device
If an open-circuit occurs at A in the above diagram, a sneak circuit will be created
in the direction of the arrow, and even though the circuit is open, a voltage will
exist. This voltage will be approximately 1/3 to 1/2 of the output of the input
devices in the part of the circuit that is not open. (The same will apply if an open
circuit occurred at B.) With such a voltage present in the circuit, the open-circuit
will not be detected. When voltage input is being supplied, either set up the input
devices so that they are not using the same power supply, or use isolators for
each input.
Section
Actual input
Input after averaging
Time
Analog Input Unit
Internal
circuits
Voltage
occurrence
7-1