Archive for Signal Conditioners

Isolated DC Signal Conditioners Applications

Value of Isolated 4ma to 20ma Signal Conditioners

DC signal conditioners with 4mA to 20mA outputs provide the ability to send signals over long wires to more than one instrument.  The current from the signal conditioner is a constant current proportional to the signal into the signal conditioner.  The constant current allows long leads.  The level of the measured signal is proportional to the voltage drop across the resistor in the input of the instrument receiving the signal.  Voltage drops across the long wires have no effect on the constant current.  The constant current allows several instruments to have their inputs wired in series and the current through each input is identical.

Isolated Signal Conditioners provide a further important value.  The isolation circuit has no direct electrical connection between the input and output circuits.  The input signal is passed through a transformer as an AC signal or through an optical isolator as a light beam.

These two types of circuits make the signal conditioner able to have a high voltage common mode signal while still processing a very low level signal from a sensor or other instrument.

The isolation from input to output also keeps extraneous currents from odd sources from flowing on the common signal lead through the signal conditioner.  This extraneous current is usually called a “ground loop”.  The isolation breaks this ground loop.

Prevent Ground Loops

A typical ground loop is created when a thermocouple has its welded junction grounded to earth through its mounting hardware.  The thermocouple signal is very low in amplitude.  If the thermocouple wire has a completed circuit from the thermocouple mount to the earth at the signal conditioner and a current flows in the thermocouple wire, it will impose a voltage on the thermocouple signal.  The typical ground loop noise is caused by AC current flowing in the wire.  With an isolated signal conditioner, there is no path for current to flow to earth at the conditioner.  The isolator breaks the ground loop.  The thermocouple signal is amplified and passed on through the isolation circuit to the conditioner output with no noise from the ground loop.

Process Small Signals On High Common Mode Signals

A common mode signal is a signal which is connected to both inputs of a signal conditioner and the conditioner has an output equal to a zero input.  An example would be a thermocouple welded to the positive terminal of a 138V battery so the temperature of the battery terminal can be ascertained.  The conditioner processes the thermocouple voltage but is not affected by the 138VDC common mode voltage from the battery.

Another example would be a battery with a resistor in series with the + terminal.  A signal conditioner can measure the voltage drop across the resistor so the current through the resistor can be determined.  The measurement is unaffected by the battery 138V common mode voltage.

A great value of isolated signal conditioners is that common mode ranges of 1000V to 2000V are not difficult to find.

Split One Signal into Many Separated Individually Isolated Signals

A common requirement of 4mA to 20mA outputs from DC input isolated signal conditioners is a need to measure 1 sensor and send the signal to a number of locations in the 4mA to 20mA form.

One method of creating several isolated signals is to connect the inputs of several 4mA to 20mA input/output signal conditioners in series.  Each conditioner will provide an isolated output.

Multiple output conditioners are available.  If dual output conditioners are used as above, one gets 2 outputs per each input.

Another method is to use one 4ma to 20mA input conditioner.  Using voltage input conditioners with 4mA to 20mA outputs, connect the voltage inputs in parallel across the input of the current input conditioner. 250 ohm loads are common inputs for current inputs.  This creates 1 to 5V drop across the 250 ohm resistor.

Isolator Creates a Separately Isolated Signal From An Existing Signal With No 2nd Power Supply Required

In areas where power is lacking and another isolated signal is required, a loop powered isolator can do the job.  A loop powered isolator uses the 4mA to 20mA current from a signal conditioner to power another circuit to create another isolated output.


MM/FR Series DR Series DM Series SR Series TW8 Series

Mighty Module

DR Series DIN-Mod
SR Series TW8 Series

Monitor Flow and Level Wirelessly at Remote Sewage Lift Stations

Monitor Flow and Level Wirelessly at Remote Sewage Lift Stations

Back in the late 1980’s a local city municipality had six lift-stations wired underground directly to their Wastewater Plant located a few miles north of Daytona International Speedway. However, in 1995 a forest fire burned the entire surrounding fields which destroyed the Level and Flow sensors and the underground wires going to the wastewater plant were melted and rendered useless.

Cost issues have been a concern for this more rural municipality. They were searching for a more economical and cost effective way to retrofit the three lift stations than reinstalling all the old hardwired systems.

Over the years, all six of the lift-stations have been repaired and upgraded. However, they have only hardwired three of the main lift-stations back to the Wastewater Plant using a data acquisition system.

The city would like to tie the remaining three lift-stations into their data acquisition system by using Wireless Telemetry. By doing this they will be able to monitor two 4/20 mADC signals coming from a Flow and Level sensor at each of the three remaining lift-stations.

The decision to use Wireless was made to help alleviate the destructive issues from the aforementioned forest fire as well as help maintain the integrity of the system given Florida’s high winds (upturned tree roots), excessive high level ground water, and encroaching metropolitan development.

All three lift stations are located about 1,000 feet apart from each other deep into the forest. However, there is a 40 foot wide clearing next to the lift-stations which the city keeps mowed as an access road to each lift-station.

DR9011 With 3 Element Yagi Antenna

DR9011 With 3 Element Yagi Antenna

In order to test the effectiveness and durability for the new proposed wireless system one of the remote non-wired stations was configured in the following manner:

·        3-Element, 8 dBi Gain Yagi Antenna was installed on a small 10 foot tower at one lift-station

·        A DR9011 wireless transmitter was installed in the existing enclosure along with the Flow and Level sensors producing the 4/20 mADC signals.

·       A DR9021 Wireless Receiver was mounted approximately 3000 ft away at one of the main lift-stations.

DR9021 Wireless Receiver

DR9021 Wireless Receiver

·        The 4/20 mA signals out of the DR9021 Receiver were wired directly into the existing data acquisition system to be sent back to the Wastewater Plant for monitoring.

The system has been running trouble free for over two years (2012) and the two other wireless systems are due for installation when time and funds are available.

Note: The lift station supervisor said that by using the Wilkerson Instrument Company wireless system they will be saving the City over $25,000 for the 3 installations.


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