Manufacturer’s specifications provide much information about how an interface device is correctly and safely used. The specification places certain limitation, not only on the module, but also on the field equipment that it can operate. The following is a list of some typical manufacturer, I/O specifications.
1.Nominal input voltage: This ac or dc value specifies the magnitude and type of voltage signal that will be accepted.
2.On state input voltage range: This value specifices the voltage at which input signal is recognized as being absolutely on.
3.Nominal current per input: This value specifies the minimum input current that the input devices must be capable of driving to operate the input circuit.
4.Ambient temperature rating: This value specifies what the maximum temperature, of the air surrounding the I/O module, should be for best operating conditions.
5.Input delay: This value specifies the time duration for which input signal must be ON before being recognized as a valid input. This delay is a result of filtering circuitry provided to protect against contact bounce and voltage transients. This input delay is typically in the 9 ms to 25 ms range.
6.Nominal output voltage: This ac or dc value specifies the magnitude and type of voltage source that can be controlled by the output.
7.Output voltage range: This value specifies the minimum and maximum output operating voltages. An output circuit rated at 120V ac, for example may have an absolute working range of 92 V ac (min) to 138 V ac max.
8.Maximum output current rating per output and module: These values specify the maximum current that a single output and the module as a whole can safely carry under load (at rated voltage).
9.Maximum surge current per output : This value specifies the maximum in rush current and duration (for example 20A for 0.1 second) for which an output circuit can exceed its maximum continuous current rating.
10.Off-state leakage current per output: This value specifies the maximum value of leakage current that flows through the output in its OFF state.
11.Electrical isolation: This maximum value (volts) defines the isolation between the I/O circuit and controller’s logic circuitry. Although this isolation protects the logic side of the module from excessive input or output voltage or current, the power circuitry of the module may be