Why Can't SSR Output Modules Be Used with Certain DAQ Devices? Hardware: Signal Conditioning Other>>SSR Series
Problem: A note on the SSR modules page in the National Instruments (NI) Catalog states:
Solution: SSR output modules do not have TTL inputs. The SSR manufacturer, Grayhill, does not claim that they do (as shown in the "Manufacturer Data Sheets" section of the SSR Series Modules and Backplanes User Guide). Unfortunately, the SSR specifications given on page 453 of the NI 2000 Catalog claim that input "logic levels" are "0 to 5V, TTL," which is incorrect. Nonetheless, the note cited above is correct. The data acquisition devices listed in the note use a third-party integrated circuit for digital input/output (DIO) interfacing. This integrated circuit conforms to TTL current and voltage specifications; however, it cannot reliably sink enough current to activate the non-TTL input of an output SSR. Other DAQ devices (such as those not listed above) use a National Instruments custom-designed integrated circuit. This integrated circuit conforms to the TTL specification, plus it can sink enough current to be used with all SSR modules sold by National Instruments. In other words, the third-party integrated circuit conforms to the TTL specification; our custom-designed integrated circuit exceeds the TTL specification. Compared to the third-party integrated circuit, our custom integrated circuit is more expensive, and thus is not used in all our DAQ products. Related Links: Grayhill Web Site Attachments:
Report Date: 02/29/2000 Last Updated: 12/26/2002 Document ID: 1USCSR0W |
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