New generation power analyzer
PM6000 has the power to provide:

• Up to 6 wattmeter channels
• 0.02% basic accuracy for definitive power loss and efficiency measurements
• Sampling at 40MHz (5MHz minimum) for error-free results
• Outstanding rejection of common-mode signals for accuracy in all applications
• A bright color display and intuitive menu system for ease of
• useConnectivity: RS232, Printer, Ethernet, USB* (*Future Release)

Overview
The AT3600 is the industry standard for testing wound components.

• Fast and highly Accurate , 10 standard tests per second at a basic 0.05% accuracy
• Integral 20 node matrix to test 10 windings in 4 wire Kelvin mode
• Integral 5kV AC/ 7kVDC Hi-Pot
• Easy operation in Production Lines with Pass /Fail indication
• Stand-alone or network capability with PC software
• Easy to program Editor Software package with graphic Winding diagrams
• Server Software exports results for 100% Quality Auditing.
• Un-beatable Testing Specifications: DC-3Mhz, 1nH-1MH, 1mV-270V, 1mA-250A DC Bias with additional DC1000.
• Testing Solutions for Laminates, Ferrites, Chokes, Current Transformers, Telecom & Audio.
• Over 40 different Tests to match your measurement needs

Overview
Precision 0-25A DC Bias Current Source with 3MHz Bandwidth

• Applies bias current to chokes and transformers so that inductance can be tested under working conditions. (0-25A with 10mA resolution)
• World’s first bias unit stackable to 250A! (10 units in parallel)
• BREAKTHROUGH DESIGN - smaller, lighter, easy to connect and use than any other bias source.
• Can be used stand-alone with almost any LCR meter and in production testing with the AT3600 and Ati transformer testers.
• Replacement for WK, HP and other manufacturer’s designs.
• PC sweep software included for plotting inductance vs. DC bias current

Rapid-Test RT-2M, a fast voice band generator & analyzer, is a black box type instrument with an easy to integrate user interface. The RT-2M is optimized for integration into production lines and network administration systems. It provides engineers with a complete performance test including such as frequency response, idle channel noise, vibra-call, ringer test, melody analyzis and DTMF. The RT-2M automatically captures, stores and analyzes the incoming signal and sends the results back to the controlling PC. The typical measurement cycle time is less than 1 second. Product-details • 12 measurement functions • dual channel architecture • multitone technologie • remote control via IEEE-488 • built-in microphone power supply

Fast 2-channel voice frequency test system. The RT-2X comprises analog, digital interfaces (ISDN,T1) with the capability to evaluate all important voice frequency performance parameters of a telecommunication device within fractions of a second.It is a complete, optimized system with a remote controlled generator as well as an intelligent analyzer for analog and digital mode operation. Numerous built-in different impedances for the analog I/O allow to match almost all national standards.Product-details • ISDN • T1 • (PCM) • DTMF generation & analysis • 2 channel • receive / transmit • digital & analog • test time < 1 sec

Emulator and Debugger for Philips P8RF5000 Smart Card Microcontrollers

Audio tools that fit into the palm of your hand. Your ideal companions for checking, maintaining and repairing of audio systems out in the field.

Minilyzer ML1 is the state-of-the-art analog audio analyzer that fits into the palm of your hand. It provides you with a comprehensive set of functions essential for the analysis of professional audio systems. The powerful Minilyzer continuously measures the signal and displays the desired results with all complementary information on an illuminated hi-res graphical LC-Display. The Minilyzer with software V2.00 (or higher) and the MiniSPL are forming a comprehensive integrating sound level meter. Product-details Measurement functions:

Level RMS, Relative • Sound Pressure Level • Distortion Analyzer (THD+N) • VU & PPM Meter • Speaker Polarity Test (for all speaker types) • Signal Balance Error • Frequency-/Time-Sweep Recording • 1/3rd Octave Spectrum RMS & SPL • Scope

Minirator MR1 is the powerful analog audio generator providing a comprehensive set of analog audio test signals as required by a professional audio environment. This handy tool enables you to stimulate any analog device with a broad range of appropriate signals for performance checking, maintenance and repairs. Convenient reliable and optimized - Minirator fits into your pocket as well as in your budget. Product-details

Signals: • Sine Wave • Square Wave • Frequency Sweep • White Noise • Pink Noise • Polarity Test Signal

Digilyzer DL1 provides a comprehensive set of analysis functions for digital audio and video related audio signals. It handles virtually all digital audio formats including ADAT and sampling frequencies up to 96 kHz. The simple and intuitive operation allows to monitor, analyze and troubleshoot any digital signals. The Digilyzer is a handheld, battery powered device with optional mains power supply.

Product-details: AES3, S/PDIF, TOS-Link • ADAT Interface • Sampling Frequency 32-96 kHz • Digital Audio Analysis • Carrier Status Analysis • Carrier Signal Measurement • Dual Domain Monitor Speaker • Comprehensive Event Logger AES3, S/PDIF, TOS-Link
ADAT Interface
Sampling Frequency 32-96 kHz
Digital Audio Analysis
Carrier Status Analysis
Carrier Signal Measurement
Dual Domain Monitor Speaker
Comprehensive Event Logger

The MiniSPL is a battery powered measuring microphone. Together with the Minilyzer they are forming an integrating sound level meter. Additionally it may be operated as a stand-alone microphone e.g. connected to a balanced audio-line, a microphone-input or a sound-card.

Product-details: • battery powered • no Phantom power required • 1/2" microphone, Class 2 acc. IEC 60651 • omni-directional • supplied with Mic clamp, wind protection • individual calibration chart included

PPA2500 Series Precision Power Analyzers
KinetiQ: DC and 10mHz to 2MHz power analysis

As with our PSM range of Phase Sensitive Multimeters, our priority when designing the user interface of the PPA2500 was to combine great flexibility with ease of use. The result is an instrument providing a greater range of functions than any competitive product and yet all primary measurements can be seen instantly by pressing just one of six mode keys.

Features

• 0.04% basic accuracy
• Frequency range dc and 10mHz to 2MHz
• High precision internal shunts
• 5 millidegree basic phase accuracy
• 30Arms - 300Apk direct current input
• 1, 2 or 3 phase versions
• Real time datalog and integration
• High speed sampling on all channels
• 1000Vrms - 3000Vpk direct voltage input
• True real time analysis with no measurement gap
• Easy to use - Single button access to all measurement modes
• Real time Digital, Tabular, Graphic and Oscilloscope displays
• Master - slave configuration for 6 phase operation
• Simple BNC connection of N4L shunts for high current applications
• RS232, IEEE488, USB, LAN, Torque, Speed and Extension ports

Watts, Volts, Amps, VA, VArs, Vdc, Adc, Vac, Aac, Vpk, Apk, Asurge, pf, frequency, phase, impedance, datalog, integration, fundamentals, harmonics

Ordering information
PPA2510: Single phase precision power analyzer
PPA2520: Two phase precision power analyzer
PPA2530: Three phase precision power analyzer

PSM1735: Frequency Response Analyzer
NumetriQ: 10μHz - 35MHz Phase Sensitive Multimeter

PSM1735 NumetriQ is the latest addition to the N4L range of phase sensitive multimeters, providing engineers with an exceptionally versatile measurement instrument.
As with other N4L products, PSM1735 NumetriQ utilises the latest DSP and FPGA technology to optimise the use of its analogue hardware providing speed and measurement flexibility without compromise on the performance of each measurement function.
Versatility without compromise
In a world where engineers from many different application areas require ever increasing speed, flexibility and measurement accuracy, N4L introduce a new generation of versatile measurement instruments that offer leading performance in every mode without the compromise on accuraccy of the additional cost that is commonly associated with such flexible instruments.
Proven technology
Utilising the latest DSP and FPGA technology to optimise the use of innovative analogue hardware, many measurements functions can be derived with great precision from the basic elements of true rms voltage on two measurement channels plus the phase angle between them. It is from this fundamental relationship between independent voltages and their relative phase angle that the phrase 'Phase Sensitive Multimeter' was derived and this is also the key to the unique combination of performance, versatility and value provided by the PSM range.
Whether you will make use of just one or all six of the primary measurement modes included in the PSM1700 and PSM1735, you can be sure of exceptional accuracy, speed and ease of use that only the latest design technology can provide.
Features

• Frequency Response Analyzer
• Vector Voltmeter
• LCR Meter
• RMS Voltmeter
• Power Meter
• Harmonic Analyzer

Dual Frequency Selective Level Meter

The SLM2200 uses powerful DSP analysis to deliver accurate measurements quickly and easily. Believed to be the only dual frequency selective level meter available, it simultaneously analyses for two independent frequency components. The noise rejection of the processing allows signals to be measured even when buried in wideband noise. True real-time processing (no missed data) with a selectable filter time constant allows measurements to be made even with varying signals. The isolation of the inputs allows connection of the SLM2200 in any environment up to 500V cat II.

The automatic tuning algorithm scans a frequency range for two frequency components. The SLM2200 then tunes the center of the passbands to the frequency of the two components present using a series of narrowing sweeps with increasing resolution. Once the frequencies have been determined, the magnitudes are monitored and displayed in real time.
Despite it's sophisticated measurement capability it is very easy to use. The versatile graphic display allows results to be viewed as graphs, multiple data values, or large single values as appropriate.
The generator on the SLM2200 uses high-speed direct digital synthesis (DDS) to provide a variety of waveforms.
The SLM2200 is designed, manufactured
& supported in the UK

Features

Includes frequency scan and automatic centering.
• Measures frequency and magnitude of two unrelated frequency components, even when lost in noise.
• Two isolated input channels rated at 500V cat II.
• Scans frequency range then centres automatically on the largest peaks.
• Magnitude displayed in dBm or V.
• Selectable bandwidth.
• Also includes 2 channel wideband true RMS voltmeter and DSO.
• Generator includes FSK simulation.
• 100μV to 500V peak signal input range.
• 10mHz to 2MHz frequency range.
• RS232 and printer port.
• Graphic electroluminescent display.
• Audible signal on any measurement.
• Convenient, portable tower format.

Example display: SLM Graph

Versatile DFT analysis instrument using DSP & FPGA technology with modern analogue techniques for optimum performance, speed of measurement and convenience.

Transformer analysis

Transformer parameters often vary with operating conditions, particularly frequency. When testing a transformer with QuanteQ the conditions are continuously variable from 10mV to 10V peak (200mA peak current) and 100mHz to 2.4MHz. An automatic frequency sweep can be used to measure any ac parameter over a frequency range and the results may be viewed on screen, or printed out as tables and graphs. Also, QuanteQ can detect the frequency from the circuit under test so that the transformer parameters may be measured under actual operating conditions.

TAF01

TAF01 is designed for testing transformers with 2 or 3 windings. Relays within the base unit make the appropriate connections for the test to be made. The base unit accepts customized jigs with ZIF sockets for quick testing of standard transformers, or Kelvin clip leads (supplied), to connect the non-standard transformers. Using the RS232 port of QuanteQ , a PC may conduct a series of tests without any manual input; PC software, CommTEST, can test the measurements against pre-set pass/fail limits.

TAF02

TAF02 has two vertical probes to energise coils or wound transformers without cores. The number of turns of a single winding or turns ratio of two windings may be measured and a shortened turn may be detected by measurement of Q factor. Supplied with Kelvin Clips, test leads or small 'grabber' test leads.

Overview

Laboratory power amplifiers

LPA01 & LPA400 are the first in a range of amplifiers developed to provide high accuracy amplification in an industrial or laboratory environment.

The LPA range

The LPA range of power amplifiers from Newtons4th Ltd are robust and reliable for use in a variety of industrial and laboratory applications. Designed originally for use with the QuanteQ and Veqtor , they can also be used anywhere where there is a need to boost a signal either in voltage or current.

They combine DC accuracy with wide bandwidth to faithfully reproduce complex waveforms, driving loads that may be capacitive, inductive or resistive.

Optionally, the DC component can be eliminated with ac coupling, or can be reduced with AC+(DC) coupling. To limit high frequency noise, the input bandwidth can be reduced with a linear phase, 2nd order, low pass filter for low frequency applications.

The amplifier gain is selectable from three precision gain settings.

LPA01

• High frequency, high current testing of wound components.
• High frequency excitation of servos and actuators up to 1A.

LPA400

• High voltage, high frequency calibration.
• Driving high voltage actuators (e.g. piezo) up to 400V.

Features

• DC accurate and wide bandwidth
• Switch selectable coupling options: AC, AC+DC or AC with reduced DC.
• Switch selectable precision gain settings.
• Switch selectable bandwidth.
• High slew rate.
• 1A continuous output current @ up to ±12V peak (LPA01).
• ±400V peak, 50mA rms (LPA400).
• ±180V peak, 100mA rms (LPA400B).
• Unconditionally stable into any load.
• Isolated from ground to prevent earth loops.
• Robust metal enclosure

Will fit underneath QuanteQ or Veqtor to boost output capability.

World Wide AC Power Supply / Frequency Converter / Inverter on your bench or in your test rack 

Power Supply CE marked World Wide AC Power Supply / Frequency Converter / Inverter on your bench or in your test rack 

Low Cost, Solid State AC Source with Direct Digital Synthesizer for Measurement and Control.

1350VA, AC Power Supply / Frequency Converter / Inverter in a 3.5"H Chassis

Behlman's BL1350 AC Power Supply / Frequency Converter / Inverter, requires just 3.5" of rack height, and weighs just 40 pounds, yet it delivers 1350 VA of quality AC power. In the BL 1350, you'll find the quality features you expect from Behlman, fully adjustable frequency and voltage, total harmonic distortion of less then 0.5%, high efficiency, plus excellent line and load regulation. There's also a unique overload protection system that folds back the voltage to maintain maximum rated current without output wave form distortion and analog remote control. For rack mounted or bench top power, no AC source combines small size, high efficiency and low cost like the Behlman BL Series. 

Features

• 1350VAina 3.5" chassis under 45 pounds
• Parallelablefor additional power or for 3 phase output
• Uniqueoverloadprotection prevents output distortion
• Remote DC programming for voltage and frequency
• TrueRMSreadoutof voltage and current

BL HP SERIES
High Power AC Power Supply / Frequency Converter / Inverter without the High Price

Behlman's high power, AC Power Sources / Frequency Converters / Inverters, combine the smooth, clean power of a linear supply with the compact design of a switching power supply. They're about one-third the size and half the cost of other AC Sources. All models come standard with variable voltage and frequency, external sync and 0-10 Vdc remote control, optional IEEE488 or RS232 interface for computer controlled. LabWindows and LabView  drives available. Small size, quiet operation and high efficiency make the high power BL Series ideal choices for precision avionics, ATE and industrial products testing requirements.

Features

• Compact and rack mountable, 67% smaller than competitive units
• Low cost per VA
• Computer controlled waveform switching delivers smooth, efficient power
• Multi-pulse input transformer offers low harmonic distortion
• Available with an IEEE488/RS232 interface
• LabWindows compatible

THE WORLDWIDE CHOICE FOR QUALITY AC POWER

Behlman's BL-PLUS Series High Power AC Source/ Frequency Converter provides the performance of a linear with all the benefits of a switching amplifier. Instead of relying on large, noisy motor generators for AC power, today's testing facilities are switching to quiet, compact Behlman AC Power frequency converters. Behlman's Solid-State BL-PLUS offers greater energy efficiency, reduced downtime, and a significantly smaller footprint. They're ideal for avionics, airborne and shipboard equipment as well as international products testing. The BL-PLUS even comes with an optional computer control for Automatic Test Equipment (ATE) application. It's adjustable voltage and frequency provides maximum flexibility.  Combined with The efficiency of the BL-PLUS Series and the savings in converting from a motor generator really add up.

Features

• Precise Adjustable Power: Variable amplitude & frequency with performance quality of a linear and the benefit of switching technology
• Small Footprint: 120KVA is only 27"Wx36"Dx78"H
• Low Input Current Distortion: Multi-pulsed input transformer and soft start circuitry assures that it will not adversely affect other equipment on the power line

Line Drop Compensation for Remote Regulation

Precision, High Quality AC Power Supply /Frequency Converter / Inverter for computer controlled applications

Behlman AC Power Supply/Frequency Converter / Inverter, programmable AC power Source delivers pure, clean, linear power. Models provide from 250VA to 9 KVA of power at output frequencies from 45 to 10,000 Hz. The ACP Series combines highly advanced magnetics with solid state circuitry and computer programmability, IEEE488 Interface included.

Features

• Typical 200% peak short-term current capability,
  up to 120% of rated current output for maximum of one half hour
• 100% rated power output available into any power factor load-unity to zero, leading or lagging
• Electronic overload and short circuit protection with instantaneous automatic recovery when overload is removed
• Actual measurements reported over IEEE488 interface and on front panel display
• Event programming optionally simulates line dropouts, transients and surges
• Built in measurement capability eliminates need for external support equipment
• Independent or simultaneous control of 3 phase voltages

DC/AC Inverter, produces  AC Power from your DC source or Battery bank

Behlman's INV series, INVERTERS deliver 1200 VA of 120 Vac, 60 Hz power in a 3.5 inc. high rack mount chassis. The Inverters operate from either 48 Vdc, 125 Vdc or 250VDC. You have a choice of a low distortion, sinewave output, Model INV1200 or a well regulated quasi-sinewave output, Mod

FEATURES

• 1200 VA in a 3.5" high chassis
• Sinewave or Quasi-Sinewave Output, Isolated and Floating
• 100% of Rated Power into any Power Factor Load.
• Crest Factor, 3:1

Produces  AC Power from your DC source / Battery bank or AC source. Zero switch over time.
AC prefered option available, consult factory.

Behlman's   ACDC - INVERTERS delivers 1200 VA of 120 Vac, 60 Hz power in a 5.25" high,19" rack mount chassis. The ACDC - INVERTER can cold start (boot) on  AC or DC Input ( 48, 125 or 250 VDC ).  In the event of loss of AC input, the ACDC - Inverter will automatically switch to your DC Battery in ZERO time. The  INVERTER continuously conditions the incoming power, providing a high quality sinewave output with very low distortion.

Features

• 1200 VA in a 5.25" high chassis
• Sinewave Output, Isolated and Floating
• Cold Start on AC or DC Input
• Automatic switch-over from AC to DC in ZERO time
• AC, DC, Output and System failure monitoring via contact closure

RUGGED, LIGHTWEIGHT, ON-LINEUPS OFFERS FAIL SAFE EQUIPMENT PROTECTION ECONOMICALLY

Behlman's PowerUPS series delivers the greatest value in true on-line, uninterruptible Power Supply/Frequency Converter/Voltage Converter at the least possible cost. This advanced, full feature UPS features digital microprocessor technology combined with a state-of-the-art IGBT inverter to provide true on-line full time power conditioning and fail safe equipment protection. The PowerUPS features a pure sinewave output, brownout protection with true voltage regulation and extensive computer and network support software. The PowerUPS combines a small, rugged design and an incredibly small price.

Features

• 650VA to 1100VA in 3.5" rack height
• 1500VA in 5.25" rack height
• True On-Line design
• Full time power conditioning
• True voltage regulation
• Fault-tolerant, fail safe design
• Extended battery options
• DOS, Windows, Novell and UNIX software interface and shutdown
• Frequency Converter

The coupling networks CDN 31 and CDN 33 are used in conjunction with the EFTC 30 burst generator

The coupling clamp CCS 30 are used in conjunction with the EFTC 30 burst generator for injection of burst pulses on non-mains cables.

Full Windows based creation and editing
Includes mathematical and drawing tools
Full waveform conversion and management
Direct import from Tektronix DSOs
Supports RS232 or GPIB interfaces
Supports all TTi products with arb capability
Demo version available - click here

10MHz D.D.S. function with arbitrary
0.1mHz to 10MHz range, 7 digit resolution.
Direct Digital Synthesis: stability & resolution
Eight standard waveforms, plus "complex" waveforms, true arbitrary waveforms and noise.
Powerful modulation modes including Sweep, AM, Gating, Trigger/Burst, FSK and Hop.
Variable symmetry, variable start/stop phase.
Programmable via RS-232 or GPIB interfaces

13MHz dual generator, digital control
0.01Hz to 13MHz frequency range
Traditional analogue generator, digital control
Dual generator architecture
GPIB interface as standard (IEEE-488.2)
Frequency stabilisation to high accuracy
Full amplitude and frequency modulation
Comprehensive triggering and gating facilities

10MHz to 1000MHz frequency range
1kHz setability, +/-2ppm frequency stability
-127dBm to +7dBm amplitude, 0.1dB steps
FM modulation, internal or external
80 character back-lit LCD display
Keyboard and rotary encoder control
Remote control options

0.005Hz to 5MHz frequency range
Built-in 7 digit frequency counter
Digital frequency lock for exceptional stability
Simultaneous display of frequency and voltage amplitude or offset
Internal/external AM up to 100%
Precision internal lin/log sweep

20MHz dial set

0.1Hz to 10MHz frequency range
Independent control of pulse delay
50ns minimum pulse width
Squarewave, double pulse & delayed pulse
Free-run, gated and triggered modes
50 Ohm output: 0.1V to 10V amplitude
TTL/CMOS and Sync outputs

Single outputs, 30V/1A, 18V/3.3A, 56V/1.1A
Single, dual or triple outputs, 30V/2A
Independent digital voltage and current meters for each output with 3 digit resolution
Constant voltage or constant current operation
Switchable 3.3V/5V output at 1A (EL302T)
Compact design uses less bench space
DC output switch, automatic mode indication

Single, Dual or Triple isolated outputs, 0 to 35V at 0 to 5A or 0 to 4A
Independent digital voltage and current meters for each output with 3 digit resolution
Constant voltage or constant current operation
Switchable 3.3V/5V output at 5A (EX354T)
Compact lightweight design with low heat output
DC output switch, automatic mode indication

Single output high power, 0 to 18V at 0 to 10A or 0 to 42V at 0 to 10A
Independent digital voltage and current meters for each output with 4 digit resolution
Switchable remote sense terminals
Constant voltage or constant current operation
Compact lightweight design with low heat output
DC output switch, automatic mode indication

High power 35V/10A & 18V/20A
Compact & lightweight high power units
35V-10A & 18V-20A models (single output)
Bench or rack mounting, front & rear terminals
Very low noise, excellent transient response
Comprehensive protection including OVP trip
High setting resolution, remote sense terminals

Dual isolated outputs, 175 watts max. each
PowerFlex design gives variable voltage & current
combinations within the range 0-35V, 0-10A.
Guaranteed 5A capability at 35 Volts
Maximum current of 10A below 12 Volts
Variable OVP trips
Precision control & metering, remote sense
Compact half-rack 3U case size

32V/1A to 32V/3A; LED displays
Wide model range, single, dual or triple outputs
Separate digital meters for voltage and current
Twin 3 digit meters with 12.5mm LEDs
0.1% accuracy, 10mV and 1mA resolution
Parallel, series and tracking modes
High current 5V logic output on triples

32V-3A single, dual & triple
Specifications as per PL bench series
RS-232 and GPIB interfaces as standard
GPIB interface conforms to IEEE-488.2
Settable voltage and current levels
10mV and 1mA programmable resolution
Readback of voltage and current via the bus

Dual 30V/2A series or parallel operation
Dual isolated outputs (0-32V, 0-2A each)
GPIB interface as standard (IEEE-488.2)
Total control from front panel or GPIB
Full voltage and current readback
Relay switched series and parallel modes
Variable OVP trip, full thermal protection
Compact half-rack 3U case size

5 digits (±210,000 counts), auto/manual range
1μV, 1nA, 1mOhm resolution, 0.012% accuracy
Wide range of computing functions included
Automatic data logging functions included
Integral True RMS AC converter
Isolated addressable RS232 interface standard
Model with GPIB (IEEE-488) interface available

Compliance quality measurements
Measures peak or rms voltage or current, real or apparent power, power factor, phase etc.
Tabular/histogram of 40 harmonics
Voltage/current waveforms with masks
Wide range of power connectors available
320 x 240 pixel high-contrast display
GPIB, RS232 and printer interfaces

Provides an EN61000–3–2 compliant source
1000W power capability at 230V
Up to 4·4A rms load current and up to 10A peak currents
Comprehensive overload protection
Connection via standard power connector

Suitable for full conformance measurements Conformance to CISPR 16 from 9kHz to 30MHz 16A continuous current rating Built-in switchable limiter and attenuator Remote control of line source Artificial hand network Wide range of connectors available?16A line impedance stabilisation network

0.1% basic measurement accuracy
Dual 5 digit high brightness displays
Automatic component recognition
Built-in 4 terminal component fixture
Limits comparator with 8 Pass bins plus 2 Fail bins
Three test frequencies, switchable bias
RS232 interface standard

High basic accuracy of 0.1%
Wide range of 1μ Ohm to 20k Ohm
Current reversal switch for detecting thermal emf effects
Current diversion switch for easy zero-ing
Four terminal measurement using Kelvin clip leads
Battery operation with built-in charger
20mV clamp for ‘dry circuit' testing