Clarke-Hess 255 Digital Wattmeter

The Clarke-Hess 255 is a True RMS digital Volt-Ampere-Watt meter designed for precise measurement of AC and DC electrical parameters. It offers high accuracy and stability, making it suitable for demanding test and calibration applications where waveform and power factor independence are critical. The instrument is capable of measuring voltage, current, power, and power factor across a wide range of values and frequencies, with features that allow for increased resolution in specific measurement scenarios.

### Technical Specifications

* **Measurement Capabilities:** True RMS measurements of Voltage, Current, and Power. Measurements are largely independent of waveform shape and power factor.
* **Frequency Response:**
* Voltage and Current readings: Typically within 1% up to 400 kHz for sine waves.
* Power measurements: Can be within 2% for a 100 kHz square wave.
* DC to hundreds of kilohertz.
* **Display:**
* Four-digit LED display.
* Full-scale values of 5000, 2000, and 1000 digits, depending on the function.
* Automatic decimal point placement.
* LED indicators for: NEGATIVE power/power factor, INPUT OVERLOAD, OUTPUT OVERLOAD, and MILLIWATTS.
* **Ranges:**
* **Current (Full Scale):** Four ranges from 5 mA to 5 A.
* External shunts or transformers can extend ranges to 50 A or 500 A.
* **Voltage (Full Scale):** Three ranges from 20 V to 1000 V.
* External voltage dividers can extend ranges up to 3500 V.
* **Power (Full Scale):** Twelve ranges from 100 mW to 5000 W.
* Full-scale power is the product of the full-scale voltage and current ranges.
* **Power x 10 Ranges:** Twelve increased resolution ranges from 10.00 mV to 500.0 W, available when both input voltage and current are less than 40% of their full-scale values.
* **Accuracy:**
* Voltage and current readings typically within 1% up to 400 kHz (sine waves).
* Power measurements within 2% for 100 kHz square waves.
* Specific accuracy details vary by function, range, and frequency. For example, for sinusoidal inputs between 30 Hz and 25 kHz:
* V.A. (Product of Volts and Amperes): ±0.6% V.A. (30 Hz – 26 kHz), ±1.5% V.A. (25 kHz – 50 kHz), ±2.5% V.A. (50 kHz – 100 kHz).
* Power: ±0.7% FS (30 Hz – 26 kHz), ±0.8% FS (25 kHz – 50 kHz), ±1.5% FS (50 kHz – 100 kHz). (FS = Full Scale of the Power range, which is the product of the Current range and Voltage range).
* **Input Impedance:** 5 MΩ for voltage terminals.
* **Circuit Loading:** Negligible circuit loading due to high input impedance and low voltage drop across current terminals (100 mV full-scale).
* **Peak Input Handling:**
* Can measure “pulse” or “spike” inputs with peak values up to 3.5 times the full-scale DC level.
* Peak-to-peak values around a zero average can be up to seven times the full-scale DC level.
* **Common Terminal Voltage:** Up to 250 Vrms (400 V peak) above the grounded case at frequencies up to 600 Hz.

### Electrical

* **Power Requirements:**
* Selectable line voltage operation: 95-105 V, 105-125 V, or 210-240 V.
* Line frequency: 50-60 Hz.
* Specify line voltage and frequency when ordering.

### Interfaces and Options

* **Analog Output (Optional):** Optically isolated analog output board providing a 1-volt output for a full-scale display reading of Current, Voltage, or Power.
* **Digital Outputs (Optional):**
* Parallel, four-digit, isolated BCD output.
* IEEE-488 Talker/Listener board.
* **Remote Control (Optional):** Provides remote control of functions.
* **Pulse Output (Optional):** Isolated pulse output.
* **External Shunt (Optional):** For extension of current measurement ranges.
* **External Transformer/Voltage Dividers (Optional):** For extension of voltage measurement ranges.
* **Front Panel Fuse (Model 256 only):** Current input fuse located on the front panel (Model 255 has an internal fuse).

### Physical

* **Construction:** Heavy-duty aluminum case.
* **Display Units:** Four identical 10.9 mm (0.43 inch) high, seven-segment, high-efficiency LED units.
* **Dimensions:** Not specified in available data.
* **Weight:** 4.1 kg (9 lbs).

### Applications

The Clarke-Hess 255 is suitable for measuring a wide variety of non-sinusoidal and low power factor waveforms, including applications such as:
* Switching power supplies
* Transformer losses
* Fluorescent lamp ballasts
* R-C filter rectifier circuits
* SCR circuits
* Mercury-arc lamp circuits
* Servo systems
* Motor testing
* Ultrasonics
* MOV (Metal Oxide Varistor) loss testing
* Automatic test equipment
* Sodium lamp ballasts
* Ferrite core losses
* Television set losses
* Electric automobile efficiency measurements

### Compatibility

* **Power Source Compatibility:** Capable of measuring AC and DC parameters.

Why Choose Aumictech for Clarke-Hess 255?
At Aumictech, we specialize in supplying high-end electrical test and measurement equipment. Whether you need precise AC/DC power analysis, advanced waveform measurement capabilities, or reliable calibration support for your testing infrastructure, our team ensures the Clarke-Hess 255 delivers maximum performance and accuracy for your critical applications.