Measurement Computing USB-TEMP-AI - Manual (Page 16)

USB-TEMP-AI User's Guide Signal I/O Connections
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Wiring configuration
Connect the semiconductor sensor to the USB-TEMP-AI using a single-ended configuration, as shown in
Figure 10. The device provides
+5V and GND pins for powering the sensor.
Figure 10. Semiconductor sensor measurement configuration
The software outputs the measurement data as a 32-bit floating point value in either voltage or temperature.
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 kΩ 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 USB-TEMP-AI digital I/O terminals to detect the
state of a TTL-compatible device. Refer to the schematic shown in Figure 11. 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 11. Schematic showing switch detection by digital channel DIO0
Caution! All ground pins on the USB-TEMP-AI (pins 9, 19, 22, 27, 30, 33, 36, 39, 49) 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
DAQ Signal Connections (available on our website at
www.mccdaq.com/signals/signals.pdf ).
Configuring the DIO channels to generate alarms
The USB-TEMP-AI features eight independent temperature alarms. All alarm options are software
configurable.
When a digital bit is configured as an alarm, that bit will be configured as an output on the next power cycle and
assume 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 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 both in data logging mode and while attached to the USB port on a computer.