BRAIN analog output voltage switch
Overview
Signaling using a 4–20 mA current loop is the most popular industrial implementation for communication between two devices because this type of port can detect if a cable is cut or shorted, and cable losses (e.g., due to cable length) are compensated for by the loop. It is, however, critical to ensure that the analog input is within the specifications of the output driver.
The Brain module has a maximum resistance (or impedance) that it can drive with each analog output. Some devices (such as valves) may have a high impedance that is too much for the analog output to drive all the way and only part of the output range will work.
The Brain’s analog outputs for serial number 5180 and higher can be configured to drive from either a 12 V source (the default setting on BRN modules from EMIT) or an 18 V source to support higher impedances.
12V and 18V switch
If all analog devices have an input resistance of 400 ohms or less, the 12 V setting should be used. If, however, the inputs driven by the BRN have an input resistance between 400 ohms and 700 ohms, and they can tolerate a momentary input voltage of up to 18 V, the BRN module should instead be configured to drive from an 18 V source. Digital Valve controller and pneumatic positioners often don't specify their input resistance. if their spec calls for more than 8.5V minimum voltage at the controller input terminal, the BRN should also be configured for 18V.
Configuring the BRN Module for 18 V To configure the BRN module for 18 V, fully unplug the module. Remove the screws from one side of the module end caps, pull off the end cap, and carefully lift the module’s top cover. The printed circuit board (PCB) is now exposed.
Locate DIP switch SW4 (see figure). Using a small screwdriver, flip the switch to the 18 V setting. Reassemble the module and plug it back into the panel.
CAUTION: printed circuit boards are sensitive to electrostatic discharge and moisture. Avoid touching the pcb itself and avoid the pcb getting wet.
Validating the 18 V Output To verify that the outputs are now driving at 18 V instead of 12 V, remove the plug from one of the AOUT terminals (e.g., pins 76–79 or 41–44). Turn on the BRN power switch and measure the voltage between one of the AOUT terminals and ground.
With nothing connected to the AOUT, the measured voltage should be approximately 18 V if the DIP switch was set correctly. Otherwise, it will read approximately 12 V. Note that this test will only work if the output is configured / assigned to a loop, otherwise it will show 0v in all cases.
