Servo - May 2009

FIGURE 3

FIGURE 4

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in LabVIEW in the DAQ Assistant setup by inverting the input lines just as you would a digital output line.

Turn The Tables

An AC input module is shown in Photo 5. It has an input rating from 90 VAC up to 140 VAC on terminals #1 and #2. Crydom offers other input modules in this AC product line up to 280 VAC. This module also has an open collector output and can be wired to the USB-6008( 9) digital input terminals as shown in Figure 4. Just like the DC input module, the AC input module’s output is inverted from what the user would normally expect and can be inverted in LabVIEW in the DAQ Assistant setup.

Conclusion

With the help of SSRs and input modules, the USB- 6008( 9) unit can control AC and DC loads and inputs from AC and non-TTL DC signals. In most cases, low voltage TTL signals are not used outside of the PC since they are too low and are susceptible to noise. Also, 5 VDC is not directly available from batteries and standard wiring systems found in homes and businesses. Then, there’s always the real danger of voltage spikes and unsuitable voltage levels getting back into your interfacing circuit and PC. Next time, we’ll cover the analog inputs and outputs of the USB-6008( 9) units. SV

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