CWTLF
The CWTLF is a flexible, clip-around Rogowski probe with an extended low frequency bandwidth.
This wide-band AC current probe is ideal for power frequency and harmonic current analysis or measuring long duration pulses.
Product Synopsis
CWTLF - Shielded / Low Frequency Models
An easy to use flexible, clip-around Rogowski coil.
The CWTLF is a flexible, clip-around Rogowski probe with an extended low frequency bandwidth. This makes it ideal for power frequency and harmonic current analysis, measuring long duration pulses, or measuring large magnitude fault currents with frequency components of just a few Hz.
A wide-band AC current probe optimised for lower frequency measurements, it has a BNC output to connect to most types of oscilloscope or data acquisition devices.
Key Features
- Predictable phase response from sub-Hz to > 100kHz.
- Low droop distortion for measuring long current pulses.
- High frequency operation into MHz.
- Current ratings from 300A pk to 300kA pk.
- Standard coil length (circumference) of 300mm to 1000mm, but longer coil lengths readily available.
- Coil insulation 10kV peak.
- Electrostatic shielded Rogowski coils to attenuate interference from 50/60Hz voltage sources and fast voltage transients.
Applications
- Power frequency 50/60Hz measurements and higher order harmonics
- Measuring large currents at very low frequency such as motor/generator fault or short circuit currents. There is no de-rating at low frequency compared to current transformers.
- Pulsed currents, and pulsed power measurements with longer duration pulses.
- Measuring small AC currents in the presence of large DC currents (e.g. monitoring capacitor ripple).
- Measuring currents in difficult to reach conductors such as tightly packed bus-bars.
Standards and Compliance
- CE marked
- Complies with EMC EN61326-1
- Complies with IEC 61010-1; IEC 61010-2-032
- PEM Ltd is certified to the ISO9001:2015 standard
PEM are committed to delivering the highest level of quality to our customers, read more about how we strive to achieve this in our Quality Standards and Compliance sections.
Key Features
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Predictable phase response
Predictable phase response from sub-Hz to > 100kHz
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Low droop distortion
Low droop distortion for measuring longer pulses.
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Wide-bandwidth
(-3dB) range from 0.008Hz to > 1MHz dependent on the current rating.
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Current ratings
Current ratings from 300A pk to 300kA pk.
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Insulated coil
Coil insulation 10kV pk.
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Electrostatically shielded coil
Excellent immunity to interference from fast local dV/dt transients or large 50/60Hz voltages.
Patented Technology. -
Customise cable length
Longer cables than the standard 1m, 2.5m and 4m are available on request.
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Custom coil length
Coil lengths longer than the standard 300mm, 500mm, 700mm and 1000mm are available on request.
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Bespoke options
Choose from a range of standard options or create a custom design.
Performance
CWTLF Models
| Model | Sensitivity (mV/A) | Peak Current (A) | Noise(mVp-p) | Droop (%/ms) | LF (-3dB) (Hz) | Peak di/dt (kA/μs) | HF (-3dB) Bandwidth
(MHz)
|
|---|---|---|---|---|---|---|---|
| CWTLF/1 | 20 | 300 | 15 | 0.47 | 0.5 | 2.5 | 1.6 (300) |
| CWTLF/3 | 10 | 600 | 15 | 0.24 | 0.25 | 5.0 | 1.6 (300) |
| CWTLF/6 | 5.0 | 1200 | 15 | 0.19 | 0.2 | 10 | 1.6 (300) |
| CWTLF/15 | 2.0 | 3000 | 15 | 0.09 | 0.1 | 11 | 1.6 (300) |
| CWTLF/30 | 1.0 | 6000 | 15 | 0.045 | 0.05 | 11 | 1.6 (300) |
| CWTLF/60 | 0.5 | 12,000 | 15 | 0.018 | 0.02 | 11 | 1.6 (300) |
| CWTLF/150 | 0.2 | 30,000 | 15 | 0.009 | 0.01 | 20 | 3.2 (300) |
| CWTLF/300 | 0.1 | 60,000 | 10 | 0.007 | 0.008 | 20 | 3.2 (300) |
| CWTLF/600 | 0.05 | 120,000 | 5.0 | 0.007 | 0.008 | 20 | 3.2 (300) |
| CWTLF/1500 | 0.02 | 300,000 | 4.0 | 0.007 | 0.008 | 20 | 3.2 (300) |
Higher Peak Current than 300kA pk available on request.
Lower Peak Current measurements with optimised low frequency performance, see the LFR range. Contact us for details of the LFR Range.
Noise - ‘Noise’ is the internally generated integrator noise, this is predominantly the same frequency as the LF (-3dB) bandwidth.
HF(-3dB) Bandwidth - The HF(-3dB) is quoted for a 2.5m cable.
di/dt ratings
These are ‘Absolute maximum di/dt ratings’ and values must not be exceeded.
| Type | Abs. Max. peak di/dt | Abs. Max. rms di/dt |
|---|---|---|
| CWTLF/1 to CWTLF/60 | 11kA/µs | 0.8kA/µs |
| CWTLF/150 and above | 20kA/µs | 0.8kA/µs |
Technical Specifications
CWTLF Models
- Output
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±6V pk corresponding to ‘Peak Current’ into ≥ 100kΩ (recommended e.g. DC1MΩ oscilloscope).
The CWTLF is not recommended for driving a 50Ω load - Accuracy
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Calibrated to ±0.2% reading with conductor central in the Rogowski coil loop.
Conductor position in the coil (for a 10mm dia. conductor) typically ±1% reading.
Linearity (with current magnitude) 0.05% reading. - DC offset
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±3mV max. at 25°C
- Temperature
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Coil and cable -20°C to +100°C
Integrator electronics 0°C to +40°C - Coil voltage
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10kV pk -- Safe peak working voltage to earth.
Rating established by a 15kV rms, 50Hz, 60sec voltage withstand test.
The CWTLF coil includes a removable silicone sleeve which provides additional robust mechanical protection. - Cable length
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1m, 2.5m or 4m (length of cable from coil to electronics).
(Longer cables are available on request). - Coil length
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300mm, 500mm, 700mm or 1000mm.
(Longer coils are available on request). - Battery Options
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BAlkaline Batteries -- 4 x 1.5V AA alkaline batteries.
External power adaptor disconnects batteries and powers unit.RRechargeable Batteries -- 4 x 1.2V NiMH batteries.
External power adaptor trickle charges batteries and powers unit.External power adaptor available in US, EURO, UK & AUS versions as an optional extra.
Dimensions
CWT / CWTHF/ CWTLF / CMC Dimensions
Coil Length and Sizing Guide
As a general 'guide to sizing' the coil, it will fit a circular conductor with a maximum diameter
= [Coil length / 3.3]
Standard Coil Lengths
300mm
500mm
700mm
1000mm
Longer coils can be made to meet specific requirements.
Minimum Bend Radius
What is included?
The CWTLF is supplied with some standard items so your measurement is ready to go the moment you receive your probe.
Details of how to specify a CWTLF probe including peak current rating, coil circumference, cable length and the type of batteries to power the electronic integrator can be found in the performance section.
If you want to purchase a CWTLF you can get a quote, if your requirement is outside that listed on our website please contact us to discuss your requirements and application.
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CWT Probe
Clip-around Rogowski coil, with cable connected to an electronic integrator housed in a plastic enclosure. The enclosure has an output BNC socket, ON/OFF switch, slide panel for batteries and socket for external DC power.
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0.5m BNC Output Cable
Every CWT unit is supplied with a detachable 50ohm BNC to BNC output cable. (The CWTMini50HF output cable is fixed).
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Carry Case
Robust hard plastic carry case with handle to protect the CWT probe in transit. Dimensions: 330mm x 265mm x 58mm.
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Batteries
Choose from either (4 x 1.5V Alkaline) or (4 x 1.2V NiMH) Rechargeable AA Batteries. (The CWT has trickle charge capability for the NiMH battery option).
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Calibration Certificate
Every unit is supplied with a fully traceable calibration certificate.
Customise & Options
PEM can customise CWTLF current probes, and supply optional items, that may be required for your specific measurement.
Customisation can be as simple as choosing coil lengths or cable lengths outside those specified on the datasheet, or you may have more complex requirements, see custom designs for some examples.
Additional optional items for the CWT range include a low noise wall mount power adaptor.
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Longer Cables
Longer cables are available up to 10m.
(Custom lengths available on request) -
Longer Coils
Longer coils are available up to 7000mm.
(Custom lengths available on request) -
Power Adaptor
External power adaptor available in US, EURO, UK & AUS versions as an optional extra.
Get a Quote
Build your CWT product options and complete our online quotation form.
Custom Design
We can provide custom designs for one off applications or volume manufacture.
Downloads
For more information and documents please see our full technical resources area.
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Datasheets
XX21S and XX13S - Power Adaptor Technical Specification Datasheet PDF 575KB Updated: 20th November, 2024
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Datasheets
CWTLF Datasheet PDF 1.8MB Updated: 28th November, 2024
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Instruction Sheets
CWT / CWTHF / CWTLF Instruction Manual PDF 718KB Updated: 20th November, 2024
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Dimension Drawings
CWT / CWTHF/ CWTLF / CMC Dimensions PDF 418KB Updated: 26th May, 2024
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Technical Notes
Voltage Immunity PDF 1.4MB Updated: 22nd October, 2024
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Technical Notes
Low Frequency Performance - 01A PDF 1.6MB Updated: 22nd October, 2024
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Compliance
CWT / LFR / CMC / DCFlex Warranty PDF 197KB Updated: 9th January, 2025
Get a Quote
Build your CWT product options and complete our online quotation form.
Technical Resources
Browse our extensive resources of technical information, insights and test data.
Applications
For more information on possible and suitable applications please review the applications below and click each one for further information.
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EMC Applications
EMC Applications
The wide-band CWT range is a versatile tool in EMC measurement applications.The CWT range has been used in a wide variety of EMC applications. It has a wide-bandwidth from sub Hz into the MHz range and configurable current ranges from less than 1A to >100kA.
Two examples demonstrate the versatility:
- The CWT has been used as the reference measurement in EMC magnetic impulse immunity testing where the DUT has to continue operation in the presence of a local impulse for several kA
- The CWT has also been used in many EMC traction applications where a measurement of mA level currents at frequencies > 1kHz need to be resolved in the presence of large 16.6 or 50/60Hz currents.
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Large AC Currents
Large AC Currents
Ideal for large AC currents in generators, motor drives and power supplies.Unlike other forms of current measurement the size of the sense coil (the Rogowski coil) is independent of the size of the measured current. Thus for large currents the size of the Rogowski coil can be chosen to suit the conductor diameter, whereas probes based on magnetic materials such as hall effect become increasingly bulky and expensive at larger current ratings.
Over a 1000A range there really is no better alternative to a PEM Rogowski current probe.
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Asymmetric Fault Currents
Asymmetric Fault Currents
Fault currents with a slow decaying DC component and AC ripple occurring in large power systems.Asymmetric fault currents occurring in large power systems, or when short circuit testing a generator or motor, typically comprise a slow exponential decay DC component with a time constant of between 10 and 100ms, with a 50/60Hz waveform superimposed.
Rogowski probes are AC current probes but the CWT LF range has an extended low frequency bandwidth, significantly less than 0.1Hz for the majority of the current range. This extended low frequency performance limits the distortion when measuring long duration pulses such as the dc component of current in these fault current applications.
Due to the high tolerance to which the LF (-3dB) performance is specified in the CWT LF the low frequency limitation, termed droop offset, is predictable and can even be compensated when post processing results.
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Small AC on Large DC Currents
Small AC on Large DC Currents
Examples including measuring small ripple currents on a large magnitude DC bus.Rogowski current probes do not measure the DC component of a current. However unlike a current transformer or a fluxgate device they contain no magnetic materials so are unaffected by the DC current. Therefore it is possible to use a small, flexible, Rogowski coil to measure a small AC current in the presence of a large DC current, whereas a sensor based on a magnetic principle would be expensive and bulky to prevent saturation effects. One such common application is measuring the ripple current in capacitors where the main current is DC or slow time varying.
Compliance
We prioritise compliance with industry standards ensuring all products are safe.
Quality Standards
We are committed to delivering the highest standards of excellence to customers.