Written by Grant Maloy Smith, the data acquisition expert

In this article we will discuss how electrical current is measured with respect to Data Acquisition (DAQ) applications today, with enough detail so that you will:

• See which current sensors and transducers are available today
• Learn the basics of accurate current measurement
• Understand how various sensors are applied in current measurement applications

Are you ready to get started? Let’s go!

## Introduction

Like voltage, current can be alternating current (AC) or direct current (DC). The electrical current is the intensity or rate of flow of an electric charge. Similar to measuring the voltage, we sometimes need to measure very tiny currents, i.e., in the microamp range, while other times we may need to measure very high currents into the thousands of amperes.

To handle this wide range of possibilities Dewesoft offers a variety of current transducers and sensors, which have a voltage output or current that is compatible with one of the voltage signal conditioners available for our data acquisition test equipment.

Dewesoft DAQ systems can measure electric properties of all major types, including voltage, current, and more. This combination of sensor and signal conditioner seamlessly converts a wide range of currents to a low-level output which can be digitized for display, storage, and analysis.

But which sensor should you choose? The purpose of this article is to describe the different kinds of current sensors available, their pros and cons, and which applications each type handles best.

## What is Electrical Current?

As mentioned above, the current is the intensity or rate of flow of an electric charge. In DC systems, the current flows in one direction, aka “unidirectionally.” Common sources of DC current include batteries and solar cells.

AC vs DC current

In AC systems the current reverses directions at a given frequency. In our businesses and homes, we have AC power based on either 50 or 60Hz (depending on your country). This Alternating Current is typically sinusoidal (e.g. in the shape of a sine wave).

The most typical source of AC is your local power plant. The current created by photovoltaic cells is DC and must be inverted to AC in order to power our homes. The same is true of a UPS, or computer battery backup system -- energy is stored in a battery and must be inverted to AC in order to provide household power.

Alternating current is also used in a non-sinusoidal fashion to modulate information onto the circuit such as in radio signals and transmission of sound.

Typical audio signal

The International System of Units (SI) term for current is Ampere, commonly abbreviated to the word “amps” and written with the symbol A.

Current is also often written with the letter I. This goes back to the French phrase intensité de courant (“current intensity” in English). Both A and I are acceptable abbreviations for current.

AC current and DC current are often abbreviated as AAC and ADC, respectively.

One ampere equals one coulomb of electrical charge moving past a given place in one second (one coulomb contains roughly 6.242 × 1018 electrons).

A current always produces a magnetic field. The stronger the current, the stronger the field. By measuring this field using various techniques: Hall Effect, Induction, or magnetic flux, we can measure the electron flow (current) in the electric circuit.

## How Can We Measure Current?

Since current always creates a magnetic field, there are Hall Effect and other sensors that allow us to measure this field and thereby measure the current.

It is also possible to connect a shunt resistor within the circuit itself and directly measure the current, as in the classic ammeter and current shunt. We will look at both methods in the sections that follow.

Dewesoft PRO Training > Voltage Measurement

Dewesoft PRO Training > Current Measurement

## Open Loop vs. Closed Loop Current Sensors

You may hear about the open-loop and closed-loop current sensors. What are the differences?

Open-loop current sensors are less expensive than closed-loop varieties such as Zero Flux current sensors. They consist of a Hall effect sensor mounted in the gap of a magnetic core. The output from the Hall effect sensor is amplified and measures the field created by the current without making any contact with it. This provides galvanic isolation between the circuit and the sensor.

Open-loop current sensor

Some open-loop current sensors have compensation electronics that help to offset the drift caused by changes in ambient temperature. Compared to closed-loop sensors, open-loop sensors are smaller and less expensive. They have low power requirements and can be used for measuring both AC and DC currents. At the same time, they are not as accurate as their closed-loop cousins: they are subject to saturation and provide inferior temperature compensation and noise immunity.

Closed-loop current sensors employ a feedback control circuit to provide an output that is proportional to the input. Compared to open-loop sensors, this closed-loop feedback design inherently provides enhanced accuracy and linearity as well as better temperature drift compensation and resistance to noise.

Closed-loop current sensor

With open-loop sensors, drift caused by temperature, or any non-linearities in the sensor will cause an error. On the other hand, closed-loop sensors employ a coil that is actively driven by creating a magnetic field that opposes the current conductor’s field. This is the “closed-loop” that provides enhanced accuracy and saturation performance.

So which is better? This depends entirely on the application. The lower cost, size, and power requirements make open-loop current sensors very popular. This is offset somewhat by the fact that their susceptibility to saturation means that they must be “oversized” in some applications in order to avoid this problem.

Closed-loop current sensors are the clear favorite in applications that require the best possible accuracy and resistance to saturation, or which are used in environments with wide temperature extremes or electrical noise.

Open-loop current sensors are found in applications like:

• Battery-powered circuits (due to their low power profile)
• Drive applications where torque accuracy need not be high
• Fan and pump current measurement
• Welding machines
• Battery management systems
• Variable speed drives
• Uninterruptible power supply applications

Closed-loop current sensors are found in applications like:

• Variable speed drives (when accuracy and linearity are paramount)
• Servo controls
• Overcurrent protection
• Ground fault detectors
• AC and DC industrial drives
• Robot control
• Energy measurement applications

As with every sensor, the desired end result should be the driving factor in choosing a sensor type.

## Current Measurement Applications

As a fundamental component of electricity, current and accurate measurement is essential in countless applications. Can you imagine a power company not knowing how many amperes it is generating? Or that they wouldn’t know how much energy its customers were using?

That would be absurd, of course. But there are millions of other purposes and requirements for current measurement. In fact, these requirements can be categorized as either open loop or closed loop.

Note that this is not to be confused with an open loop or closed loop sensors, as described in the previous section. Here we are talking about the current measurement application itself as being either open or closed loop.

In a closed-loop current measurement application, we need to know the current because we need to control it in real-time. Applications include:

• Components where the current must be limited not to exceed a certain level, e.g., switching power supplies and battery chargers, to name a few.
• Automatic shutdown functions of critical systems based on the current draw.
• Current-controlled solenoid valves used in automobiles, aircraft, etc.
• The power amplifier biases current control.
• And many more.

In open-loop current measurement applications, there is no requirement for real-time control, but we need to know the current value for a variety of purposes, including:

• R&D on electro-motors in automobiles, trains, consumer products, etc.
• Energy consumption for revenue purposes.
• Testing the performance of actuators used in aircraft, rockets, etc.
• Measuring the current supply and consumption of electric trains and the third rail and catenary systems that power them.
• Power quality applications for both producers and consumers of energy.
• Literally millions of applications in research, manufacturing, automotive, aerospace, military, health sciences, education, industrial automation, and more.

## Major Current Sensor Types

Different current sensors and current transducers are thus available for these various methods, each adapted to the measuring environment as well as the current range that is intended to be measured. For example, the requirements for measuring microamps (µA) are greatly different from those required to measure thousands of amps. We will look at each sensor type and describe its theory of operation as well as its application.

Shunt Hall Effect CT Rogowski Zero Flux
Connection Type Direct Indirect Indirect Indirect Indirect
Current AC and DC AC and DC AC AC AC and DC
Accuracy High Medium Medium Low High
Range Low Medium High Medium High
Drift Low Medium Medium High Low
Isolation No 1) Yes Yes Yes Yes

1) Shunts can be isolated via either an internal or external signal conditioner, but they are not inherently isolated

As mentioned earlier, there are two major methods of measuring current:

• By direct contact with the current (aka a shunt/ammeter)
• By measuring the electromagnetic field or flux of the current

## Direct Contact With the Current

The most common way to measure current is to connect the ammeter (a meter to measure current) or shunt resistor in series with the circuit. An ammeter or ammeter shunt is really nothing more than a highly accurate resistor. When we place a precision resistor across a circuit, a voltage drop will occur across it. The shunt sensor’s output is measured by the data acquisition system, which applies Ohm’s law to determine the amperage flowing through the circuit.

Note that the maximum current range that a given ammeter is capable of measuring is limited by its resistor’s value. Therefore a common practice is to add an additional shunt resistor in parallel to increase the maximum measuring range of our test equipment.

This limitation is why the direct connection to the electrical conductors of a circuit is more widely used in low current applications, but rarely in high current applications, where indirect measuring sensors like current clamps and flex coils are far more prevalent.

## Shunt Current Measurement

When you connect a low ohm resistor in parallel with a circuit, the current flows through the shunt resistor -R- and generates a voltage drop.

Typical shunt measurement hook-up in a simple circuit

We can measure this drop and apply Ohm’s law to calculate the current.

Graphical representation of Ohm’s Law

Ohm’s law describes the relationship between voltage (V), current (I), and resistance (R). If we know two out of three of those, we can easily calculate the third via simple arithmetic. The diagram above illustrates the three ways that Ohm’s law can be expressed:

I = V/R  OR  V = IR  OR R = V/I

So if we know the voltage (drop) and resistance, we can calculate the current using I = V/R.

The shunt resistor should be chosen for the appropriate voltage range and current range, because too high of resistance will affect the measurement, and will also waste energy and distort the measurement as the resistor heats up. This energy loss is equal to:

I2 * R

In addition, the accuracy of the resistor is an important factor, since this directly affects the accuracy of the measurement itself.

Dewesoft DSIi-10A Current Shunt

Dewesoft offers several compact size current shunts, each designed with a different resistor inside, intended to measure different current ranges. These shunts have been engineered to have the least possible effect on the circuit itself.

DSI adapters can be plugged into virtually all Dewesoft data acquisition devices. The isolated analog inputs of Dewesoft amplifiers is an important factor in ensuring accurate measurements, since the shunt is connected directly to the circuit being measured, and isolation between the circuit and the measuring system is always important. Isolated inputs mean that you can place your shunt on the low-side or high-side of the circuit, and not worry about a ground loop or common-mode measuring errors.

Considering Ohm’s law again and the interlocking nature of voltage, current, and resistance, it is absolutely clear that a DAQ system must be able to make a very accurate voltage measurement and resistance measurement in order to make an accurate current measurement.

### IOLITE STG with Built-in Current Shunt

Certain Dewesoft signal conditioners have a built-in shunt for measuring small currents. Take for example the IOLITE and IOLITEd data acquisition series STG signal conditioner. This module is a universal type, meaning that it can handle a wide range of sensors and input types.

For example, it can handle strain gages in full-bridge, half-bridge and quarter bridge configurations, voltages up to 50V, potentiometric sensors, and currents up to 20 mA. In addition, DSI series adapters can be used to allow it to handle thermocouples, RTD sensors, LVDT position sensors, voltages up to 200V, currents up to 5A, IEPE accelerometers, and more.

IOLITE DAQ system with various modules

The IOLITE 6xSTG features six differential inputs with over-voltage protection and sensor power from each of its universal inputs and sample rates up to 20 kS/s/ch.

For current measurements, It has a built-in 50 Ω shunt resistor that can be applied in software, allowing engineers to measure current either up to 2 mA or 20 mA, user-selectable.

IOLITE chassis are available in an “IOLITEs” benchtop model, which accepts up to 8 multi-channel modules (seen on the picture above). For permanent installations, there is the “IOLITEr” model, made for standard 19” rack-mounting. This model has 12 slots for modules:

IOLITEr rack-mounting model

Both IOLITE models feature dual-redundant power supplies for reliable performance in critical applications. They also both have dual EtherCAT buses running in parallel. The primary bus is used for full speed buffered data acquisition to a PC computer hard-drive running DEWESoft X software. The secondary bus is mainly used for the real-time low-latency data feed to any 3rd party EtherCAT based control system.

IOLITE is a unique DAQ system that bridges the worlds of real-time control and high-speed data acquisition, combining them in one reliable instrument.

## Measuring the Electromagnetic Field Or Flux Of the Current

Because current always generates a magnetic field that is proportional to the amount of current, we can measure this field using a variety of sensors and thus measure the current.

Now let’s look at some of the most common current sensors and transducers, their basic working principles, and how they are best used.

## Hall Effect Sensor Measurement

Hall effect sensors operate in principle by measuring magnetic fields. In 1879, twenty years before the electron was discovered, American physicist Edwin Hall observed that when current flows through a conductor, the electrons move in a straight line. However, when this conductor is exposed to a magnetic field, the Lorentz force acts upon it, and the path of the electrons bends.

Furthermore, when the electrons are pushed more to one side of the conductor than the other, creating a potential difference between the two sides of the conductor. Hall observed that this potential difference was directly and linearly proportional to the strength of the magnetic field.

This potential voltage difference, as measured between sides (or “planes”) of the conductor, is called the Hall voltage.

The Hall effect has been adopted for thousands of applications, including proximity switches, motor speed control circuitry, tachometers, LVDT sensors, and even as a fuel level sensor in automobiles. But we will focus on its application specifically with current sensors.

Typical Hall Effect Current Sensor

Hall effect current clamps work by passing the conductor through their open core. They, therefore, provide a non-contact method of measuring AC and DC currents. They require very little power, so they can be powered directly from a SIRIUS preamplifier with a DSUB9 connector. No additional power supply is needed.

They are not as accurate as flux gate current clamps or zero flux transducers, but they offer a much wider measuring range.

Hall effect sensors are available in both open-loop and closed-loop varieties. Closed-loop sensors add a compensation winding and enhanced onboard signal conditioning, making them more accurate than their open-loop siblings.

DS-CLAMP-150DC DS-CLAMP-150DCS DS-CLAMP-1800DC
Type Hall sensor Hall sensor Hall sensor
Range 200 A DC or 150 A AC rms 290 A DC or 150 A AC rms 1800 A DC or AC rms
Brandwidth DC to 100 kHz DC to 100 kHz DC to 20 kHz
Accuracy 1 % + 2 mA 1 % + 2 mA 0 - 1000 A: ±2.5 % of reading ±0.5 A
1000 - 1500 A: ±3.5 % of reading
1500 - 1800 A: ±5 % of reading
Sensitivity 20 mV/A 20 mV/A 1 mV/A
Resolution ±1 mA ±1 mA ±1 mA
Overload Capability 500 A DC (1min) 500 A DC (1min) 2000 A DC (1min)
TEDS Fully supported Fully supported Fully supported
Dimensions 205 mm x 60 mm x 15 mm
(Clamp opening d = 32 mm)
106 mm x 100 mm x 25 mm
(Clamp opening d = 25 mm)
205 mm x 60 mm x 15 mm
(Clamp opening d = 32 mm)

Dewesoft brand Hall Effect Current Sensors

The DS-CLAMP 150DC and 150DCS can be connected directly to a Sirius® LV or Sirius® HS-LV amplifier with a DSUB9 connector. The DS-CLAMP-1800DC can be connected directly to all DEWESoft® amplifiers with DSUB9 connector (e.g. Sirius® LV-DB9).

Typical Hall Effect Sensor from Dewesoft

## Current Transformer (CT) Measurement

Current transformers (CTs) are used to measure alternating current (AC). They are inductive sensors that consist of a primary winding, a magnetic core, and a secondary winding.

Essentially, a high current is transformed to a lower one using a magnetic carrier, thus very high currents can be measured safely and efficiently. In most CTs, the primary winding has very few turns, while the secondary winding has many more turns. This ratio of turns between the primary and secondary determines how much the magnitude of the current load is stepped down.

Typical Current Transformer

The AC detected by the primary winding produces a magnetic field in the core, which induces a current in the secondary winding. This current is converted to the output of the sensor.

They are available as split-core configuration from Dewesoft, which allows convenient hook-up possibilities since the circuit does not need to be altered in any way. You can simply open the jaws and release them around the wire, making these AC current clamps especially convenient to use.

### Dewesoft brand CT Current Transformers

DS-CLAMP-5AC DS-CLAMP-15AC DS-CLAMP-200AC DS-CLAMP-1000AC
Type Iron-Core Iron-Core Iron-Core Iron-Core
Range 5 A 15 A 200 A 1000 A
Bandwidth 5 kHz 10 kHz 10 kHz 10 kHz
Accuracy 0.5 % for 12A
0.5 % for 5A
1% for 500mA
2% for 5mA
1% for currents of 1-15A
2.5% for currents < 1A
1% for currents of 100-240A
2.5% for currents of 10-100A
3.5% for currents of 0.5 - 10 A
0.3% for currents of 100A - 1200 A
0.5% for currents of 10A - 100 A
2% for currents < 1A
Phase ≤ 2,5° ≤3° for currents of 1-15A
≤5° for currents <1A
≤2.5° for currents of 100-240A
≤5° for currents of 10-100A
Not specified for currents of 0.5 - 10 A
0.7° for currents of 100A - 1200 A
1° for currents of 10A - 100 A
Not specified for currents of < 1A
TEDS Fully supported Fully supported Fully supported Fully supported
Sensitivity 60 mV/A 100 mV/A 10 mV/A 1 mV/A
Resolution 0.01 A 0.01 A 0.5 A 0.001 A
Overload Capability Crest Factor of 3 Crest Factor of 3 Crest Factor of 3 1200 A for 40 minutes
Dimensions 102 mm x 34 mm x 24 mm
(Clamp Opening d = 15 mm)
135 mm x 51 mm x 30 mm
(Clamp Opening d = 20 mm)
135 mm x 51 mm x 30 mm
(Clamp Opening d = 20 mm)
216 mm x 111 mm x 45 mm
(Clamp Opening d = 52 mm)

Dewesoft Iron Core CT Current Transformer

Iron Core AC current sensors offer the convenience of requiring very little power, so they can be powered directly from a SIRIUS preamp with a DSUB9 connector. No additional power supply is needed. They have bandwidths from 2 Hz to 10 kHz (2 Hz to 5 kHz for the DS-CLAMP-5AC), and up to 10kHz for the other models in the series). These clamps can be connected directly to all Dewesoft amplifiers with DSUB9 connectors (such as the Sirius-LV).

## Rogowski Current Sensor Measurement

Rogowski sensors have the advantage of going around large cable bundles, bus bars, and irregularly shaped conductors in a way that regular clamps cannot.

They’re made for AC measurements, and their low inductance means that they can respond to fast-changing currents. And their lack of an iron core makes them highly linear, even when subjected to very large currents. They provide excellent performance when measuring harmonic content. A small integrator and power circuit is needed and is built into each DS-FLEX sensor.

Typical Rogowski Coil Scheme

The number in their model name like 300, 3000 or 30,000 refers to the maximum amperage that they can read. The final number refers to the length of the “rope” in cm. So for example, the DS-FLEX-3000-80 can read up to 3000 AAC and has a “rope” length of 80cm (i.e., 800 mm or 31 inches).

### Dewesoft Rogowski Coil “FLEX” Current Sensors

DS-FLEX-3000-17 DS-FLEX-3000-35 DS-FLEX-3000-35HS DS-FLEX-3000-80 DS-FLEX-30000-120
Type Rogowski coil Rogowski coil Rogowski coil Rogowski coil Rogowski coil
Range 3, 30, 300, 3000 A
ACrms
3, 30, 300, 3000 A
ACrms
3000 A
ACrms
3, 30, 300, 3000 A
ACrms
30, 300, 3000, 30000 A
ACrms
Bandwidth 3A: 10 Hz to 10 kHz
Others: 10 Hz to 20 kHz
3A: 10 Hz to 10 kHz
Others: 10 Hz to 20 kHz
5 Hz - 1MHz 3A: 10 Hz to 10 kHz
Others: 10 Hz to 20 kHz
3A: 10 Hz to 5 kHz
Others: 10 Hz to 20 kHz
Accuracy <1.5 % <1.5 % <1.5 % <1.5 % <1.5 %
Coil length 170 mm (Ø 45 mm) 350 mm (Ø 100 mm) 350 mm (Ø 100 mm) 800 mm (Ø 250 mm) 1200 mm (Ø 380 mm)
TEDS Not supported Not supported Fully supported Not supported Not supported

Dewesoft DS-FLEX-3000 Rogowski coil current sensor

These clamps can be connected directly to all DEWESoft® amplifiers with DSUB9 connectors (e.g. SIRIUSi LV).

Note that AC current is normally output as a true RMS reading, which DC current is output as a discrete value.

## Zero Flux Sensors Measurement

A Zero Flux aka “FluxGate” current sensor is similar to a Hall effect current sensor, except that it uses a magnetic coil instead of a Hall effect system. The higher accuracy that results makes these sensors ideally suited for industrial, aerospace, and other applications that require high accuracy measurements. Zero Flux current transducers measure current with galvanic isolation. They reduce the high voltage currents to much lower levels which can be easily read by any measurement system.

Typical Zero Flux / FluxGate Sensor

They have two windings which are operated in saturation to measure the DC current, one winding for the AC current and an additional winding for compensation. This kind of current measurement is very precise because of the zero flux compensation. Why? Normally a magnetic core retains a residual magnetic flux, which ruins the accuracy of the measurement. In zero flux transducers, however, this parasitic flux is compensated for.

Zero flux transducers are ideal when high AC/DC accuracy and/or high bandwidth (up to 1 MHz). They are very linear and have a low phase and offset error. But they are not so handy for making simpler measurements that don’t require as much accuracy or bandwidth. For those applications, the current sensors in the previous sections are recommended.

Flux technology extends this principle by using a magnetic coil as a detection element instead of a Hall element. In addition, this is a closed-loop sensor, meaning that a secondary winding is used to eliminate offsets which can lead to measurement inaccuracies. Flux sensors can handle even very complex AC and DC waveforms, and are generally regarded to provide excellent accuracy, linearity, and bandwidth, and are an essential part of any power quality analyzer or power analyzer.

### Dewesoft FluxGate Current Clamps

Dewesoft offers several FluxGate current clamps that have been paired with our SIRIUS systems, including mating and power cables. These FluxGate clamps must be powered by the SIRIUSi-PWR-MCTS2 power supply unit.

DS-CLAMP-200DC DS-CLAMP-500DC DS-CLAMP-500DCS DS-CLAMP-1000DS
Type Flux gate sensor Flux gate sensor Flux gate sensor Flux gate sensor
Range 200 A DC or AC RMS 500 A DC or AC RMS 500 A DC or AC RMS 1000 A DC or AC RMS
Brandwidth DC to 500 kHz DC to 100 kHz DC to 200 kHz DC to 20 kHz
Accuracy ±0.3 % of reading ±40 mA ±0.3 % of reading ±100 mA ±0.3 % of reading ±100 mA ±0.3 % of reading ±200 mA
Sensitivity ±10 mV/A ±4 mV/A ±4 mV/A ±2 mV/A
Resolution ±1 mA ±1 mA ±1 mA ±1 mA
Overload Capability 500 A (1min) 1000 A DC 720 A DC 1700 A DC
TEDS Fully supported Fully supported Fully supported Fully supported
Dimensions 153 mm x 67 mm x 25 mm
(Clamp opening d = 20 mm)
116 mm x 38 mm x 36 mm
(Clamp opening d = 50 mm)
153 mm x 67 mm x 25 mm
(Clamp opening d = 20 mm)
238 mm x 114 mm x 35 mm
(Clamp opening d = 50 mm)

### Dewesoft Zero Flux Current Transformers

Dewesoft offers several Zero Flux current transformers that have been paired with our SIRIUS DAQ systems, including mating and power cables. These sensors must be operated with the SIRIUSi-PWR-MCTS2 or SIRIUSir-PWR-MCTS2 power supply units.

IT-60-S T-200-S IT-400-S IT-700-S IT-1000-S IN-1000-S IN-2000-S
Primary Current Range DC
RMS Sinus
60 A 200 A 400 A 700 A 1000 A 1000 A 2000 A
Overload Ability Short Time (100 ms) 300 Apk 1000 Apk 2000 Apk 3500 Apk 4000 Apk 5000 Apk 10000 Apk
Max. burden resistor (100 % of Ip) 10 ohm 10 ohm 2.5 ohm 2.5 ohm 2.5 ohm 4 ohm 3.5 ohm
di/dt (accurately followed) 25 A/μs 100 A/μs 100 A/μs 100 A/μs 100 A/μs 100A/μs 100A/μs
Temperature influence < 2.5 ppm/K < 2 ppm/K < 1 ppm/K < 1 ppm/K < 1 ppm/K < 0.3 ppm/K <0.1 ppm/k
Output Ratio 100 mA at 60 A 200 mA at 200 A 200 mA at 400 A 400 mA at 200 A 1 A at 1000 A 666 mA at 1000 A 1A at 2000 A
Bandwidth (0.5 % of Ip) DC ... 800 kHz DC ... 500 kHz DC ... 500 kHz DC ... 250 kHz DC ... 500 kHz DC ... 440 kHz DC ... 140 kHz
Linearity < 0.002 % < 0.001 % < 0.001 % < 0.001 % < 0.001 % < 0.003 % < 0.003 %
Offset < 0.025 %  0.008 % < 0.004 % < 0.005 % < 0.005 % < 0.0012 % < 0.0012 %
Frequency Influence 0.04 %/kHz 0.06 %/kHz 0.06 %/kHz 0.12 %/kHz 0.06 %/kHz 0.1 %/kHz 0.1 %/kHz
Angular Accuracy < 0.025° + 0.06°/kHz < 0.025° + 0.05°/kHz < 0.025° + 0.09°/kHz < 0.025° + 0.18°/kHz < 0.025° + 0.09°/kHz < 0.01° + 0.05°/kHz < 0.01° + 0.075°/kHz

Rated isolation voltage RMS, single isolation
CAT III, pollution deg. 2
IEC 61010-1 standards
EN 50178 standards

2000 V
1000 V
2000 V
1000 V
2000 V
1000 V
1600 V
1000 V
300 V
300 V
X X
Test voltage 50/60 Hz, 1 min 5.4 kV 5.4 kV 5.4 kV 4.6 kV 3.1 kV 4.2 kV 6 kV
Inner diameter 26 mm 26 mm 26 mm 30 mm 30 mm 38 mm 70 mm
DEWESoft® Shunt 5 Ω 5 Ω 2 Ω 2 Ω 1 Ω 1 Ω 1 Ω

## Isolation and Filtering

Isolation and filtering are critical aspects of any data acquisition instrument or test system.

### Isolation

Isolation is especially critical when making direct measurements of the circuit, i.e. using the shunt method. The isolation built into virtually all Dewesoft signal conditioners and preamplifiers is quite high and sufficient to properly isolate the measuring system from the object under test.

This ensures the integrity of your measurements and protects against short circuits. In addition, it allows you to place the shunt across either the low side or the high side of the circuit most of the time, providing additional flexibility. Low-side shunt measurements are typically preferred because the relatively low current drop across the shunt means that a high impedance output is provided to the signal conditioner. But there are two drawbacks to low-side measuring:

• The shunt will not detect a fault if the resistor gets shorted to ground
• Low-side shunts are not suitable for measuring multiple loads, or those which are turned off and on independently.

Therefore, sometimes high-side shunt current measuring is sometimes required, using Dewesoft’s differential and isolated preamplifiers.

### Filtering

Filtering is another critical function of any high-performance data acquisition system. Electrical noise and interference is an everyday challenge for test engineers. It can be induced by fluorescent lights, other electrical equipment, and countless other sources.

Dewesoft signal conditioners provide powerful low-pass filtering in hardware that allows engineers to suppress frequencies above a certain level. And in DEWESoft software, a broad palette of low-pass, high-pass, band-pass and band-stop filtering is available - and can be applied in real-time or after the measurement is done.