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Tuesday, February 26, 2019

Controlled Oven for stable Reference

This is a continuation of the previous two circuits. This circuit controls the temperature in a miniature oven that holds a stable dual voltage reference.

Controlled Oven for stable Reference

In colder seasons or locations this will maintain the temperature at a higher level. A mini fan in the equipment ensures external heat does not reach the oven, fan keeps the larger chassis cool.

Temperature Measurement and Control

This circuit may fail if the equipment is in very hot open locations, big heaters, hot machines or direct sunlight falls on equipment OR the Lab is not cooled to near normal ambient temperatures.

High Stability Reference Mirror

LM399 is a Precision Reference chip. From this a dual polarity mirrored reference is derived using OP07 op-amps. This assembly is mounted in a miniature oven to ensure temperature stability. 

High Stability Reference Mirror

The oven used Two Steel Boxes one mounted in another with Glass Wool In-between to reduce heater losses.  Steel was used to ensure excellent EMI-RFI Shielding. Both the outer and internal shell was earthed.

Instrumentation and Measurement Circuits

Regulated and Filtered Supply to this assembly further ensures consistent performance over the years and in various environments and seasons.

Sunday, February 24, 2019

Differential amplifier for HV Power Supply

This is part of a precision High Voltage but Low current Power Supply for Testing leakage currents in passive devices. This Supply is a module for a  Automatic Test system in component inspection.

Differential amplifier for HV Power Supply

HV Precision Power Supply Circuits

Insulation of Transformers and the Isolation of plastic capacitors are best analyzed by applying a High Voltage and measuring the leakage currents.

These currents are in the order of nano-amps and pico-amps; values close to the bias-currents and leakage currents of devices. Some offsets and corrections can be done in software for the ATE systems.

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