Archive for Loop Powered Isolators

DC Isolators

Wici LogoDC Isolators

Provide galvanically isolated DC Output proportional to DC Input

Wilkerson Instrument Co.     800-234-1343 Wilkerson Instrument Co Blog Page   Wilkerson Instrument Co LinkedIn Page

Isolators are used to break ground loops and to measure signals with high common mode voltages.

Ground loops are created when the source of a signal and the driven instrument have their common inputs tied to the earth at each device or the common lead is used to carry AC current for some other device.  AC current flowing in the common lead drops a small AC voltage due to the wire resistance. The voltage appears in series with the desired signal and creates “noise” on the desired signal.  The Isolator breaks the common lead and the AC current can no longer flow.

A common mode voltage is a voltage that is connected to the + and – inputs of a device.  Example – A small resistor in series with the + lead of a 138VDC battery and the – side of the battery is the “common” lead for the system.  The resistor drops a small voltage proportional to the battery current.  The Isolator can measure the small voltage across the resistor even though it is floating 138VDC above the system circuit common.

MM4380A Field Rangeable DC-DC Isolator Picture

Mighty Module Series Logo Series

MM4380A Field Rangeable Input and Output
Span ± 16mV to ± 256VDC, ± 0.8mA to ± 100mA
Offset Cancel ±110% of Span
MM4300 Factory Ranged Input and Output
Span ± 50mV to ± 250VDC, ± 1mA to ± 1ADC
MM4300A Four Models, Combinations of 4/20mA and 0/10VDC Input and Output
Mighty Module DC-DC Isolator Picture

UL/cUL Recognized
MM4380A and MM4300

DinMod Series Field Rangeable DC-DC Isolator Picture

DIN-MOD Series Logo Series

DM4380A Field Rangeable Input and Output
Span ± 16mV to ± 256VDC, ± 0.8mA to ± 100mA
Offset Cancel ± 110% of Span
DM4300A Four Models, Combinations of 4/20mA and 0/10VDC Input and Output
DM4391 Loop Powered Isolator
4/20 mADC In and Out
Linearized ± 0.02% of Span

UL/cUL Recognized
DM4380A and DM4300A

DR Series DC-DC Isolator Picture DR Series Logo

DR4380A Field Rangeable Input and Output
Span ± 50mV to ± 256VDC, ± 1mA to ± 100mA
DR4300 Factory Ranged Input and Output
Span ± 50mV to ± 250VDC, ± 1mA to ± 250mADC
DR4302

Inputs: 1/5, 0/10VDC; 0/1, 4/20, 0/20, 0/50mADC
Outputs: Dual Isolated 4/20mADC

 

UL/cUL Recognized

Silver Series DC Isolated Two-Wire Transmitter Picture

50 mm Diameter

Silver Series Logo

SR2101 Isolated 2 Wire Transmitter, Head or DIN Rail Mount
Factory Ranged Input ± 16mV to ± 128 VDC, ± 0.01mA to ± 100mADC
30th Anniversary Banner

Wilkerson Instrument celebrates 32 years experience designing, manufacturing, distributing, and providing engineering help for the process control industries.

Phone always answered by a live person

Other Products:

  • Wireless Data Acquisition and Control
  • Loop Powered Displays
  • DC Motor Drives
  • DC Isolation
  • Frequency Inputs
  • Turbine Flow Meters

 

Industries Served:

  • Water and Waste Water
  • Power Generation
  • Bottling and Food Processing
  • Transportation
  • Chemical Processing
  • (OEM) Original Equipment Manufacturer

Wilkerson Instrument Company Inc.
2915 Parkway Street
Lakeland, FL. 33811 U.S.A
Wici.com

Wilkerson Instrument Co Blog Page   Wilkerson Instrument Co LinkedIn Page

800-234-1343    863-647-2000

How Loop Powered Isolators Work

How Loop Powered Isolators Work

Loop powered isolators are necessary when an extra isolated 4/20mA output is required in areas where no power is available.

A loop powered isolator’s power is provided by its 4/20mA input current.  This makes it possible for an existing 4/20mA loop to be used to provide another isolated 4/20mA output through a loop powered isolator.

dm4391 loop powered isolator

DM4391-2 Dual channel DC isolators With and without front cover

A loop powered isolator is basically a center tapped transformer which has the input 4/20mA current flowing through its center tap on the primary. An oscillator circuit alternately switches the current through each half of the primary.  This alternating current creates a current in the secondary of the transformer. The voltage out of the secondary is rectified and filtered.

The turns ratio on the transformer is designed with a slight step down so the current out of the secondary is slightly greater than the input current.

This is a simple form of a loop power isolator, but it has shortcomings in that the transformer is not perfectly linear over the current range. The current is also sensitive to the load resistance on the secondary.

A more complex version of a loop powered isolator has basically the same transformer circuit, but it has a circuit which monitors the current into the unit. The circuit passes this data through another isolation circuit to the secondary side of the unit.  This circuit controls the current out of the isolator so it exactly matches the input current.  This control circuit makes the loop powered isolator as accurate and linear as any powered transmitter.The DM4391 utilizes this feed forward circuit to provide an accurate and linear 4/20mA output.

The DM4391 can be connected anywhere in an existing 4/20mA loop. It is available as a single channel or dual channel unit.

For specifications and information about the DM4391 see our Catalog Page (pdf) or Installation / Operation Manual (pdf)

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