Archive for Ground Loop

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

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

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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

Wilkerson Instrument Co Blog Page   Wilkerson Instrument Co LinkedIn Page

800-234-1343    863-647-2000

Ground Loop Primer

Ground Loop Primer                                                       Printer Friendly PDF

One of the most frustrating problems of the measurement and control industry is that of the ground loop. Its effects can appear and disappear with no apparent reason and can range from mere annoyance to downright destructive. It seems that ground loops carry some mystical connotation to the point that our industry has made it a “catch all” culprit for anything that cannot be explained.

While ground loops can be complex problems and may not always be predictable they can be understood and dealt with if we have a little insight into just what they are and how they can affect a transmitted signal. Let us first refer to Figure 1.

This Figure depicts what we might consider to be a typical measurement loop. It has a transmitter sending a signal to a receiver, some finite distance away, over a pair of wires. One side of the signal current has become grounded via internal circuitry and ultimately is tied to earth ground usually via the instrument case.

As depicted in Figure 1, this measurement loop would probably work fine and not have any influence from ground loop currents. However, reality sets in and we have to abide by plant safety procedures, the National Electric Code, etc. Safety procedures almost always will mandate that each piece of equipment be grounded to earth at its respective installed location. This is where the trouble starts.

Once we ground two pieces of equipment at two different locations we have set the stage for ground loop problems. If we could take a volt meter (Figure 2) with very long leads and measure the voltage between the ground points of the transmitter and the receiver we would measure some voltage.

It may measure in millivolts or it could be many volts. Either way, if there is a potential difference, then current will flow between these two points. Since the earth presents itself as a resistor between these two ground points the amount of current that flows between the points will be directly proportional to the voltage difference and inversely proportional to the resistance.

For those who are fans of Ohms Law you will recognize this equated as I=E/R. I being the ground current; E being the voltage between the ground points; and R being the resistance of the earth between the two ground points.

Ground Loop Figure 2

Figure 3 shows that we now have two currents that can flow through the wiring between the transmitter and receiver. If it all stopped here we could just calibrate the measurement loop to nullify the effects of the ground current and go on about our business.

Many times this is exactly what happens. A technician calibrates the loop and comes back a few days later to find that his calibration is no longer accurate. What has happened? It could be a lot of things. Maybe it rained and the resistance of the earth changed. Suffice it to say there are many phenomenons, either natural or man-made, that can change the resistance or the voltage between the two ground points thus effecting the calibration of the loop.

Ground Loop Figure 3

It is apparent that we are “fighting a losing battle” thinking we can anticipate the interactive affect of ground loop currents on our measurement loop. What can we do to get around this problem? The answer is to provide DC isolation between each component in our loop. (Figure 4) DC isolation can be accomplished either in the transmitter, the receiver, or with a third component as shown in Figure 4.

Ground Loop Figure 4

Figure 4 shows DC isolation being accomplished by using a transformer. An isolator module, of course, is much more than just a transformer, but it is the transformer component in a signal isolator that, in fact, provides the isolation since DC cannot pass through a transformer. Now that we have inserted this “transformer” into the circuit, the ground loop between the transmitter and the receiver no longer exists, thus eliminating its effects on the signal current.

The Wilkerson product line provides several options for implementing DC isolation depending on how the isolator is powered. There are three basic ways of powering an isolator.

These are listed below with the respective modules:

1. Input Powered or Loop Powered

DM4391-1 DM4391-2

2. Output Powered or Two Wire


3. External Powered

MM4300 Series MM4380A

DM4300 Series DM4380A


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