Calibrator
Theory of Operation
5
In-guard
From front to back, the in-guard assemblies are:
• A15 terminal indicators
• A14 output switching
• A10 TC, A3 analog motherboard
• Optional A4 scope option
• A5 impedance
•A6 DDS
• A8 HV amplifiers
• A7 current
• A12 IG power
• Mains transformer secondaries
Each of these assemblies has a detailed theory of operation. See the brief descriptions below.
A14 Output Switching
The A14 contains all the necessary switching for the various functions to the output terminals. The A14
also has some of the protection circuitry that prevents damage from situations such as connecting the
Product outputs to line voltage or other high-current power supplies. Firmware control is accomplished
with an MSP430 microcontroller via a serial link to the in-guard processor on the A6 DDS. The output
terminal binding posts are directly connected to the A14. This connection eliminates cables and
improves the reproducibility over a number of units.
A3 Motherboard
The A3 motherboard is a simple analog and digital backplane that consists only of thru-hole
connectors, a relay, and a common-mode choke. This assembly was designed to be as simple as
possible to improve reliability and reduce the possibility of manufacturing defects. It interconnects all
the in-guard assemblies and to the A9 out-guard controller.
A5 Impedance
The A5 provides synthesized equivalents of Resistance, Capacitance, and Inductance. This feature
shares some of the circuitry with the Resistance and Capacitance functions.
A6 DDS
The A6 is the heart of the analog system. The A6 provides digital control for all the in-guard assemblies
through serial links to MSP430s.
The A6 has:
• The precision, ovenized 7 V reference
• Direct Digital dual channel synthesizer (DDS)
• Precision PWM DACs for both voltage and current
• Averaging ac/dc converter for acv
• Sense dividers and buffers for acv and dcv up to 120 V
• The acv/dcv loop error integrator
• A high-resolution adc for calibration, diagnostics, and monitor functions
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