Communicating with high-side devices in a motor drive or power-converter systems.Preventing ground loops in communications networks.Protecting expensive processors and related circuits from high voltage.Protecting industrial operators from high voltage.This kind of isolation is required in a number of instances, such as: The current output is not effected by the 138VDC battery voltage.This article is part of the TechXchange : Delving into Digital IsolatorsĮlectronic isolation is a means of preventing the transfer of direct current (dc) and unwanted alternating current (ac) between two parts of a system while still enabling signal and power transfer between those two parts. The common mode capability of the transmitter allows the signal input leads to be 138VDC above ground, but it can accurately process the low voltage across the shunt resistor. The resistor drops 10mV per amp, which is processed by the transmitter and converted to the constant current output. Connect the 2W transmitter input across the resistor. 01 ohm resistor in series with the positive lead. Measure current from a 138V battery pack by putting a. It only responds to a difference in the level between the signal and common lead. The transmitter will not respond to this common mode signal. The signal input and common terminal, being tied together, both have exactly the same signal attached. If the input terminal and the common terminal are connected together, and a signal is connected to this connection, and the other signal lead is connected to its normal place, the transmitter has a common mode input. The common connection is the circuit common of the input amplifier. These are the signal input and the common connection. APPLICATIONS FOR ISOLATED DC INPUT 2 WIRE TRANSMITTERS Common Mode DefinitionĪ DC input transmitter has 2 connections for the input signal. The analog output of the D/A converter drives the current output circuit of the transmitter. The binary code, in the form of pulses, is passed on to a digital to analog converter through optical isolators. The level of the DC output is measured with an analog to digital converter. The power for this circuit requires an isolated power supply which uses a transformer for the isolation. The digital transmitter has a DC amplifier as an input circuit. This pulse is passed through an optical isolator and then converted back to a DC signal which drives the current output circuit. The output circuit must convert the square wave AC signal back to a DC voltage which can drive the current output circuit.Īnother common circuit is to convert the DC signal to a pulse signal where the data is determined by the width of the pulse. The signal out of this amplifier must be changed to a form which can be sent through the signal isolation circuit.Ī common isolation circuit is to convert the DC signal to a square wave AC signal and transformer couple it to the output circuit. ![]() It can typically be calibrated for a current or voltage input. The transmitter has a DC amplifier as an input circuit. The isolation between input and output is typically rated with an insulation capability of 1000 volts or more. The device can measure DC voltage or current inputs and provide a 4mA to 20mA output without a galvanic electrical connection between the input and output. DC INPUT ISOLATED TWO WIRE TRANSMITTER AND HOW THEY WORKĪn isolated DC input two wire transmitter is a valuable tool for many difficult measurements.
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