The Digital Input Channels
The dataTaker 50 data logger has 5 digital input channels, and the dataTaker 500/600 series data loggers have 4 digital input channels.
The digital input channels of the dataTaker share with the digital output channels.
The digital input channels are used for
monitoring bit wide and byte wide logic state inputs
low speed counting to 10 Hz
for detecting digital and counter events to trigger Schedules
The Channel Expansion Module (CEM-AD) has 20 digital input channels which can only be used for monitoring bit wide and byte wide logic state inputs. The digital input channels of the CEM-AD cannot be used as counter inputs or digital outputs.
The Analog Frequency, Analog Period, and Analog State input types can also be considered as digital inputs.
The input type identifier, units text and number of channels for the digital inputs are summarized in the table below.
* these counters share the digital input channels
Note : The digital input channels of the dataTaker and the Channel Expansion Module (CEM-AD) are powered down whenever the logger is operating in low power mode. The digital input channels will not register or count changes of state while powered down.
The high speed counters of the dataTaker remain powered at all times, and count pulses while the dataTaker is in low power mode.
The digital channels can also be used as open collector outputs to switch external devices.
The Digital Input Circuit
The digital input channels of the dataTaker and the Channel Expansion Module (CEM-AD) are TTL and CMOS compatible.
The digital input circuits have a 10 KOhm pull up resistor to 5 Volt, as illustrated in Figure 112. This forces the digital inputs to be normally high, and allows contact closures to be connected directly between the digital input channels and GND which will pull the channel low when contacts are closed.
A series 100 KOhm resistor provides input protection on the digital channels against over voltages being applied.
Figure 112 ñ Digital Input Circuit
Digital Input Sample Period
Whenever the dataTaker is operating in normal power mode, the digital input channels (and keys on the display) are read every 50 mS to detect any changes of state.
This period is referred to as the digital sample interval, and determines the minimum detectable pulse width. This facility has importance when monitoring large contacts, switches, etc. which can bounce for intervals of 10's to 100's of milliseconds on a closure.
The digital input sample period may be changed by the Parameter13 command (See Section III ñ Parameter Commands).
Using DeTransfer, the digital sample period is set by the command for example
sets the digital input sample period to 30 mS. The digital input sample period may be set within the range of 1 to 100 mS. The default digital input sample period is 50 mS.
Using DeLogger, the digital sample period is set in the Program Builder under the Settings tab. Right click the Special Commands button to open the dialog, and enter the Parameter13 command in the Pre Schedule Initialization Commands window, as shown above.
Digital Input Modes
The digital input channels of the dataTaker are multipurpose, and can be used in a number of modes as follows
used alone for monitoring logic state inputs
combined into groups of sequential channels for monitoring logic byte (nibble) inputs
used alone as low speed counters (except CEM-AD). The low speed counters may be defined as accumulating counters, resetting counters, or up down counters.
The digital inputs can be simultaneously used in more than one of these modes.
For example a digital channel can be used to periodically read the current state of a contact closure, and to count the number of times that the closure was opened or closed over a period of time.
However the individual digital input channels of the dataTaker cannot be used as both accumulating and resetting low speed counters in the same task.
The digital input channels can also be used to detect digital events (for example pulses, contact closures, etc) and trigger Schedules to read input channels and execute calculations as follows
detect external digital events for triggering Schedules
detect counter events resulting from external pulse inputs, for Schedules
detect external conditions under which Schedules can proceed
Note : These triggers can only be used while the dataTaker is operating in the normal power mode.
Connecting to Digital Input Channels
Input signals are connected to the digital input channels of the dataTaker via the screw terminals as shown in Figure 112.
Digital logic state and low speed counter inputs are connected to the digital input channels between the digital channel terminal and any GND terminal or any unused Analog Return terminals.
Logic inputs from solid state circuits can be connected directly to the digital input channels. The ground of the logic circuit must be connected to any GND terminal of the dataTaker.
Contact closures can be connected directly to the digital input channels, between the digital input channel screw terminals and any GND terminal