Part 2

Plug-In Assembly Configuration 497Before connecting loads to the assembly, it is important to select proper wire type,size and length for your application and to properly connect the SENSE lines for accurateload voltages. Even the shortest leads can degrade the VDAC performancebecause of the IR drop in the leads.For example, approximately 15 feet of 22 AWG wire has a resistance of 0.242ohms. At the full (1 5 mA) output of the VDAC, this results in a 3.63 mV voltagedrop which is more than 1 LSB. If this drop is not compensated, it results in an errorin the load voltage.For this reason, it is important to connect the SENSE leads to the load so that theVDAC output can be automatically adjusted to compensate for errors due to leadresistance. Some considerations for connecting the SENSE leads and a wire chartare shown in Figure 145.The SENSE leads (+SENSE and - SENSE) should be applied as close as possible tothe point where the voltage is to be measured. Also, the voltage drop in the HIsource line should not exceed 1.5V and the voltage drop in the LO source line shouldnot exceed 0.5V. To achieve specified voltage regulation, the HI lead resistanceshould not exceed 100 ohms and the LO lead resistance should not exceed 50 ohms.Although the load leads are shown as straight lines (for clarity), some immunity fromstray magnetic field pickup can be achieved by twisting each pair of HI (+) and LO(-1 leads.NOTEIf sensing is not used, +SENSE should be connected to HIand -SENSE should be connected to LO at the terminal block.If this is not done, voltage output errors may occur.If a shield is used for the SENSE lines, do not use the shield as one of the sensingconductors. Also, one end of the shield should be tied to the low side of the loadand the other end left unconnected. In general, it is desirable to connect the shieldas close as posssible to the low side of the load, as shown in Figure 145.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com