Frequently Asked Questions
Benchtop vs. System Loads?
Beyond power, current and voltage, there are some important trade-offs that are worth considering. Programmable electronic loads fall into two general instrument application categories: Benchtop and System. Benchtop loads are generally designed for entry-level applications that prioritize low cost. They are designed to run independently and have limited ranging and accuracy.
System loads have a different set of performance criteria. They must stand up to near-continuous usage, employ precision measurement circuitry, provide trigger signals, allow a constant-power performance range, contain a built-in transient generator, yield a minimum command processing time, and be capable of built-in test and quick calibration. Some instrumentation manufacturers present their loads as capable of meeting the requirements of both applications. While System loads can often be used in Benchtop applications, the reverse usually results in performance limitations uncovered only after substantial integration efforts are completed and product testing has begun.
At NHR, we only make System loads.
Slot vs. Modular Loads?
Slot loads have arisen from historic benchtop applications. They satisfy one set of performance criteria (voltage, current and power) and are typically used independently. Think of them as a benchtop load with a GPIB interface.
Modular loads, together with a mainframe chassis, are of more recent design optimized for both increased flexibility and higher density packaging. The latest modular loads can be synchronously paralleled (meaning that they act as a single load even in dynamic modes such as ramping and short-circuit). This feature has particular merit in applications that require frequent load reconfiguration to match the various output load profiles of multiple-output units-under-test. The benefit is that the widest amount of load configurations can now be addressed with the least number of loads. This has great value in test situations where one can't anticipate what loading will be required in the future. Another recent innovation is where individual chassis may be synchronously paralleled. This allows more power to be added painlessly in the field at a later date.
How do I calibrate these loads?
A typically overlooked issue is the ease of calibrating electronic loads once they are embedded in a test system that has near-continuous uptime requirements. Some benchtop loads still have pots that require removal and opening of the load housing for calibration. All NHR programmable electronic loads feature closed-cover calibration with non-volatile memory that stores calibration data. In this manner, loads don't have to be removed from the system and calibration is often a matter of minutes. For systems that contain many loads, NHR also offers a Precision Calibrator that accesses loads externally and then automatically calibrates 43 different load parameters with accuracy traceable to National Standards.