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California Instruments
3091LD Series

3000VA Programmable AC Loads

Product Overview
The 3091LD is designed to provide precisely controlled, non-linear loads for testing AC power generation equipment such as UPS’s and AC sources. In addition, any active or passive current carrying devices such as switches, circuit breakers, fuses, connectors and power semiconductors can be tested. Traditionally, many of these products are tested using resistive load banks. This approach does not simulate real-world conditions such as switching DC/AC converters found in many AC powered products. This type of conventional testing does not fully exercise the equipment under test (EUT) under worst case operating conditions. High peak currents and low power factor loads can significantly impact the operating characteristics of a UPS or AC power product. The 3091LD AC Load can simulate high crest factor and variable power factor load conditions. This provides an effective method of testing AC products against real-world conditions and can significantly increase product reliability. Unless properly exercised, product defects may go undetected until a unit is used at a customer site, resulting in costly field returns.

Key Features
  • Multi-mode AC Electronic Load Flexible solution for a wide range of AC power test applications
  • 3000 Watt Power Dissipation Master / Auxiliary configurations for higher power and multi phase applications
  • 50 to 350 V, 45 Hz to 440 Hz Commercial, Military and Avionics applications
  • Programmable Crest & Power Factor Test AC power products for
    real-world conditions
  • Built-in Measurements Eliminates the need for additional test equipment in bench or ATE applications
  • Remote Control IEEE-488 and RS232C Interface for automated test applications

Front Panel Control
The AC load can be operated from an easy to use, menu driven front panel. Product tests can be performed quickly in an R&D setting by punching up specific load conditions on the front panel and reading the measurement screen of the 3091LD. This fast interactive front panel control mode can be used during a product's early development cycle to isolate potential performance problems before the product leaves the engineering lab.

Automated Testing
The 3091LD can be deployed in ATE test stations using either IEEE-488 or RS232C remote control. The industry standard SCPI (Standard Commands for Programmable Instrumentation) protocol is used and instrument drivers are available to ease test software development. The built-in metering functions of the 3091LD AC load can be used to eliminate the need for additional test equipment such as meters, power analyzers and oscilloscopes. This and the reduced size of the 3091LD compared to passive load banks, represents a savings in both cost and rack space.

Power Levels
Each 3091LD is capable of dissipating 3000 W of single phase AC power. For higher power or three phase applications, a 3091LD master unit can be combined with one or more auxiliary units. The master 3091LD unit provides the required consolidated measurements so the test system controller - or the operator - need only interface to the master unit, regardless of the specific configuration. Single, split or three phase configurations can be software configured from the master 3091LD.

Measurement and Analysis
The 3091LD can be used to emulate a wide variety of AC load conditions to support real-world testing and evaluation of UPS and AC source products. Specifically, the following modes can be selected:

Common
Model Description
Constant Power CP This mode effectively emulates constant power loads such as switching power supplies.
Constant Resistance CR Emulates a conventional resistive load or power resistor. A programmable range from 2.5 Ohms to 1000 Ohms covers a wide range of applications. This mode can be used to replace conventional resistive load banks.
Constant Current CC Provides a constant current load. This mode may be used to simulate both linear (resistive) and nonlinear (active) loads for voltage regulation testing.
Constant Voltage CV This mode emulates a shunt regulator load and may be used to test current source products.
Short circuit SC Test the short circuit protection mode of the EUT by providing a short condition. The 3001LD can handle surge currents of up to 300 Amps for up to 50 msec and sustained currents of 30 Amps in this mode of operation. The low voltage cut-off of the load can be programmed from 50 Volts up

User Control
All AC load modes are easily set from the front panel using a menu-driven user interface. The large LCD screen is used to display setup information as well as measurement data. Measurements include volt RMS, volt peak, current RMS, current peak, crest factor, true power, apparent power, power factor and frequency. Both voltage and current waveforms at the load input terminals can be digitized and displayed on the front panel graphical LCD. This allows EUT output behavior to be analyzed quickly without the need to hook up additional test equipment. A Windows graphical user interface (GUI) is provided to expand the measurement and display capabilities of the 3091LD. The GUI can be used to save and print test results for report purposes.

Crest Factor and Power Factor control
When operating in constant current or constant power mode, the 3091LD supports crest factor control by narrowing the conduction angle of the current waveform in order to match the requested crest factor. Thus, the peak current is increased while retaining the RMS current level. While the apparent power remains constant, the true power decreases. This results in a reduced true power factor. Consequently, as crest factor is increased, the true power factor automatically decreases. The load further controls power factor by shifting the current with respect to the input voltage (displacement power factor). Both leading and lagging power factor control is available. A phase shift of the current is only possible if the crest factor is higher than 1.414. Thus, crest factor and power factor control ranges are coupled as shown in the graph to the right.

Instrument Control Software
The large LCD screen is used to display setup information as well as measurement data. Measurements include volt RMS, volt peak, current RMS, current peak, crest factor, true power, apparent power, power factor and frequency. Both voltage and current waveforms at the load input terminals can be digitized and displayed on the front panel graphical LCD. This allows EUT output behavior to be analyzed quickly without the need to hook up additional test equipment. A Windows graphical user interface (GUI) is provided to expand the measurement and display capabilities of the 3091LD. The ICS can be used to save and print test results for report purposes.