Figure 4 . Plots of noisy data sometimes encountered in older test setups (a) vs. much cleaner data routinely collected with the new system (b). The plot in 4b also shows data collected using N-samples-per-decade logging. Support of multiple instrument interface protocols (RS-232, RS-485, IEEE-488). It is necessary to select an instrument interface protocol to enable the computer to accept input data from the stand-alone subsystem. Several interface protocols are available on the market. For

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... purposes the most significant factors to consider were availability of inexpensive hardware, low susceptibility to noise and the flexibility to support various instrument command structures. The communication interface protocols adopted for the recent versions of GENTEST include RS-232 and RS-485. The advantages of RS-232 3 for our lab implementation included: 1. Most workstations have one or two RS-232 ports so this built-in feature was considered to be a natural contender for helping to reach our goal of simplified connectivity and interchangeability. 2. It is a well-understood technology and many instrument manufacturers offer this protocol for their equipment. 3. Many hardware options are typically available to support a variety of physical layout situations for lab or field use. A significant disadvantage of the RS-232 protocol, however, is that it was not designed to handle more than one receiver-sender pair. Moreover, we anticipated applications where signal runs could exceed the standard recommended length of about 50 feet. Furthermore, the unbalancedline signaling mode makes RS-232 subject to induced noise even for runs less than 50 feet. A related interface standard is RS-485. Though the instrument command syntax would likely be the same as for RS-232, the balanced differential signaling used in the RS-485 interface offers additional and significant advantages 4 several of which are described below: 1) RS-485 uses disconnectable line drivers which permits networking multiple subsystems (typically up to 32 receivers and 32 senders) together via simple addressing commands; Consolidation Test 4 TSF Group 1