Allen-Bradley 1771-OFE Analog Output Module
The 1771-OFE is an intelligent block transfer module that converts binary or four digit BCD values to analog signals. The 1771-OFE controls four differential voltage or current outputs. The module is available in two versions, the 1771-OFE1 for voltage outputs, and the 1771-OFE2 for current outputs. Its use with the EPICS control system supports 1 current range, and 3 voltage ranges, the voltage ranges are selectable on a per channel basis. Supported input ranges include
: Voltages Currents 1771-OFE1 1771-OFE2 --------------------------------------------------------- 1 to 5V DC 4 to 20mA 0 to 10V DC -10 to 10V DC The output specifications for the voltage ranges dictate a maximum of 10mA per channel. The output specifications for the current ranges dictate a maximum of 1200 ohms per channel of load resistance.
1771-OFE Analog Output Module Strapping
Both the 1771-OFE1 (voltage output module) and the 1771-OFE2 (current output module) have a configuration strap for the test mode output level. Only the 1771-OFE1 (voltage output module) requires the configuration of module straps for the individual channel ranges, the 1771-OFE2 (current output module) has no such jumpers. Remove the module's right hand cover plate (the one with the labels) by removing the four screws on that side. This will expose the bottom side of the printed circuit board and three more screws which must be removed for complete circuit board removal. Observe the location of the configuration jumpers in figure 6.1, and note the location of the individual channels.
The Test Mode Output jumper (1771-OFE1 and 1771-OFE2) controls the magnitude of the outputs if the module should receive a reset condition from the control system. For instance, if a module output is set for a 0 to 10V DC range, and the Test Mode Output is set to MID, if the module resets, the output will will be forced to 5V DC. If no jumpers are placed on the Test Mode Output configuration plug, the module will default to MID. Note that if Switch 1 of the DIP switch assembly on the Universal I/O chassis is set closed (ON), the module's outputs will remain in their last state ignoring the Test Mode Output Jumper.
The Range selection jumpers (1771-OFE1 only) are set individually for each channel according to the range desired as illustrated in figure 6.1.
1771-OFE Analog Output Module Installation
The Allen-Bradley 1771-OFE Analog Output Module may be installed in any Allen-Bradley Universal I/O Chassis, 1771-A1B, 1771-A2B, 1771-A3B, or 1771-A4B. Before Installation, calculate the power requirements of the modules currently in the chassis. Add to that 1.5A @ 5V DC, the current required by the 1771-OFE. Check to be sure that this combined current requirement does not exceed the current driving ability of the chassis power supply.
Module Location in the I/O Chassis
The 1771-OFE may be placed in any slot of the I/O chassis with the exception of of the extreme left slot. This slot is occupied by the Remote I/O Adapter Module. It is suggested that analog input modules and low voltage DC modules be placed away from AC modules or high voltage DC modules to minimize electrical noise interference.
The Allen Bradley Universal I/O chassis have the ability to limit the slot access to certain modules by the implementation of a keying system. Modules are slotted in two places at the edge of the circuit board. The position of the keying bands on the backplane connector of the I/O chassis must correspond to these slots. To key a slot for use by the 1771-OFE Analog Out put only, place the keying bands between 10 and 12 and between 26 and 28 on the I/O chassis backplane connector.
Before a module is inserted into the Universal I/O Chassis, be sure that the power to the chassis is shut off. This can be done without shutting off the IOC that the Universal I/O Chassis is connected to, and without removing the subnet communication link. To insert the module, place it in the plastic tracks on the top and bottom of the Universal I/O Chassis. Slide the module into the Universal I/O Chassis until the module comes in contact with the backplane connector. Do not force the module in, instead apply firm and even pressure on the module to seat it properly on the backplane connector. Snap the chassis latch over the top of the module and connect the wiring arm to the module. The Universal I/O Chassis should begin communicating with the host IOC when power is reapplied, no rebooting of the IOC will have to be done.
1771-OFE Analog Output Module Wiring Connection
Connection to the analog signals of the 1771-OFE is accomplished through the use of the wiring arm. Signals should be connected to the screw terminals on the wiring arm, as detailed in figure 6.2, and the wiring arm should be connected to the front tab connector on the 1771-OFE. The recommend cable length for voltage signals is 50ft. This is based on considerations of signal degradation and electrical noise immunity in typical industrial environments. When shielded cable is used and grounding of the shield is desired, it is recommended that the connection be made at one of the I/O chassis mounting bolts. To prevent ground loops only the chassis end of the cable shield should be grounded.
1771-OFE Analog Output Module Use
The front panel of the 1771-OFE contains a green RUN and a red FAULT indicator. At power up the green indicator will light and remain on. At power up an initial module self-check occurs. If a fault is found initially or occurs later, the red indicator will turn on.