THE USB DIGITAL INPUT MODULE

Digital inputs have only 2 states – High or Low. However, the voltage range that you apply depends totally on the application. Therefore the USB Digital Input Module is available for the various voltages threshold levels like 0-5V, 0-10V and 0-24V. The 5V threshold level has a VLowMax of 2.5V and a VHighMin of 3.5V. If a certain module has a voltage range that is below 2.5V, it is considered as a LOW state and a module that has a voltage range higher than 3.5V is considered a HIGH State. There cannot be a range that is in between the VLowMax and VHighMin. The VLowMax of 10V threshold level is 6V and its VHighMin is 8V. Also, the VLowMax of 24V threshold level is 16V and its VHighMin is 19V.

In most of the automation applications the 24V digital inputs are used generally. Therefore when you are interfacing signals of 24V inputs, if it is a LOW state, you will need to apply a voltage that is equal to or below the 16V range and if it is a HIGH state, you will need to apply 19V or less only. You cannot use a voltage that is in between 16V and 19V.

While using digital input module the input lines need to be optical as well as potential insulated. This is in order to protect your hardware and have a greater flexibility when it comes to design. You can configure any of the 4 channels that are provided by the USB Digital input modules in the following 3 modes:

• Reflect mode: This is used to sample a digital input signal. It provides a conditioned as well as a debounced state.
• Edge Detection mode: This is used in case you need to sample the digital inputs in high speed. You can detect the rising and falling edges accurately in real time
• Count mode: This acts as a high speed counter in case of digital input signals. It provides various options that can be used to evaluate a range of sensors as well as pulses.

In case of signal conditioning and debouncing you can apply filters to the input channels if you want to suppress the erroneous signal states. In case of high sampling rate, you can ensure signal detection without any activity of your host computer and this is very crucial when you want to ensure real time behavior.