Lakeshore Learning Materials 642 - Manual (Page 12)

Lake Shore Model 642 Electromagnet Power Supply User’s Manual
1-2 Introduction
Output Architecture (Continued)
The Model 642 output architecture relies on low noise, linear input and output stages. The linear circuitry of the Model
642 permits operation with less electrical noise than switch-mode electromagnet power supplies. One key benefit of this
architecture is CE compliance to the electromagnetic compatibility (EMC) directive, including the radiated emissions
requirement.
Output Programming
The Model 642 output current is programmed internally via the keypad, externally by the computer interface, externally
by the analog programming input, or by the sum of the external and internal settings. For internal programming, the
Model 642 incorporates a proprietary digital-to-analog converter (DAC) that is monotonic over the entire output range
and provides a resolution of 0.1 mA.
The Model 642 generates extremely smooth and continuous ramps with virtually no overshoot. The digitally generated
constant current ramp rate is variable between 0.1 mA/s and 99.999 A/s. To ensure a smooth ramp rate, the power supply
updates the high-resolution DAC 23.7 times per second. A low-pass filter on the DAC output smoothes the transitions at
step changes during ramping.
Output Readings
The Model 642 provides high-resolution output readings. The output current reading has a resolution of 0.1 mA. The
output voltage reading reports the voltage at the output terminals with a resolution of 0.1 mV. All output readings can be
prominently displayed on the front panel and read over the computer interface.
Protection
The Model 642 continuously monitors the line voltage, load power, internal power, and load resistance as well as a
variety of other internal circuit parameters for signs of trouble. Some fault conditions result in a warning message while
others will provide a warning message and zero the output. When hazardous conditions exist, the Model 642 will shut
itself off.
NOTE: The Model 642 is equipped with a high-line lockout circuit which will prevent the unit from being turned
on if it is connected to a voltage source that is much higher than the voltage for which it is configured.
Figure 1-1. Model 642 Front Panel