Measurement Computing WLS-TC - Manual (Page 14)

WLS-TC User's Guide Sensor Connections
14
Digital I/O connections
You can connect up to eight digital I/O lines to the screw terminals labeled DIO0 to DIO7 . You can configure
each digital bit for either input or output. All digital I/O lines are pulled up to +5V with a 47 K ohm resistor
(default). You can request the factory to configure the resistor for pull-down to ground if desired.
When you configure the digital bits for input, you can use the WLS-TC digital I/O terminals to detect the state
of any TTL-level input. Refer to the schematic shown in Figure 4. If you set the switch to the +5V input, DIO0
reads TRUE (1). If you move the switch to GND, DIO0 reads FALSE (0).
Figure 4. Schematic showing switch detection by digital channel DIO0
Caution! All ground pins on the WLS-TC (pins 9, 19, 28, 38) are common and are isolated from earth
ground. If a connection is made to earth ground when using digital I/O and conductive
thermocouples, the thermocouples are no longer isolated. In this case, thermocouples must not be
connected to any conductive surfaces that may be referenced to earth ground.
For general information regarding digital signal connections and digital I/O techniques, refer to the Guide to
Signal Connections (available on our web site at
www.mccdaq.com/signals/signals.pdf ).
Configuring the DIO channels to generate alarms
The WLS-TC features eight independent temperature alarms. All alarm options are software configurable.
Remote alarm configuration is supported.
When a digital bit is configured as an alarm, that bit is configured as an output on the next power cycle and
assumes the state defined by the alarm configuration.
Each alarm controls an associated digital I/O channel as an alarm output. The input to each alarm is one of the
temperature input channels. You set up the temperature conditions to activate an alarm, and also the output state
of the channel (active high or low) when activated. When an alarm is activated, its associated DIO channel is
driven to the output state specified.
The alarm configurations are stored in non-volatile memory and are loaded on power up. The temperature
alarms function in wireless operations and while attached to the USB port on a computer.
You can configure alarm settings when you connect the WLS-TC locally to the computer through the USB port,
or when operating it remotely through the wireless interface.