3-20 B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUALWIRING CHAPTER 3: INSTALLATION3Figure 3-16: Current through contact inputs with auto-burnishingRegular contact inputs limit current to less than 3 mA to reduce station battery burden. In contrast, contact inputs withauto-burnishing allow currents up to 50 to 70 mA at the first instance when the change of state was sensed. Then, within25 to 50 ms, this current is slowly reduced to 3 mA as indicated. The 50 to 70 mA peak current burns any film on thecontacts, allowing for proper sensing of state changes. If the external device contact is bouncing, the auto-burnishingstarts when external device contact bouncing is over.Another important difference between the auto-burnishing input module and the regular input modules is that only twocontact inputs have common ground, as opposed to four contact inputs sharing one common ground (see the ContactInput and Output Module Wiring diagrams). This is beneficial when connecting contact inputs to separate voltage sources.Consequently, the threshold voltage setting is also defined per group of two contact inputs.The auto-burnish feature can be disabled or enabled using the DIP switches found on each daughter card. There is a DIPswitch for each contact, for a total of 16 inputs.Figure 3-17: Auto-burnish DIP switchesThe auto-burnish circuitry has an internal fuse for safety purposes. During regular maintenance, check the auto-burnishfunctionality using an oscilloscope.3.3.6 RS232 faceplate portA nine-pin RS232C serial port is located on the faceplate for programming with a computer. All that is required to use thisinterface is a computer running the EnerVista UR Setup software provided with the relay. Cabling for the RS232 port isshown in the following figure for both 9-pin and 25-pin connectors.The baud rate for this port can be set, with a default of 115200 bps.
