# Presentation: 143770

## Introduction to AC-DC DifferenceThermal Convertersand AC-DC Metodologyat NIST

- Thomas E. Lipe
- Quantum Electrical Metrology Division
- National Institute of Standards and Technology
- Gaithersburg, MD 20899-8171

## Outline

- Brief introduction to thermal transfer standards
- What they are
- Why we use them
- The NIST Ac-dc Difference calibration service
- Parameter space
- Uncertainties
- Research activities
- AC Josephson Voltage Standard
- Film multijunction thermal converters
- BIVD high voltage system
- Cryogenic thermal transfer standard

## Introduction

- Customers:
- U.S. National Laboratories
- Department of Defense Laboratories
- Commercial Laboratories
- 75 to 100 Instruments per year ($150k)
- Active research programs
- ACJVS to develop intrinsic ac voltage standards based on quantum effects
- FMJTC to develop new working standards and high-current converters
- BIVD system to improve high-voltage measurements
- CTTS to develop new primary standard

## Introduction

- Thermal converters form the primary standards for calibration of
- Ac voltage
- Ac current
- Electric Power
- Electrothermal instruments
- RMS responding (direct measurement of power)
- Simple structures - readily modeled
- No mechanical effects to account for

## Introduction

- Basic thermoelement
- Rating: 1 mA - 10 mA,1 V - 4 V
- Major error sources are thermoelectric effects and low-frequency tracking of the input signal
- Used for both voltage and current measurements
- Voltage Measurements
- Use series resistors to reduce input voltage
- Major error sources are reactance and dielectric loss
- Current Measurements
- Often use current shunts with thermoelements
- Major error sources are current definition effects

## Iin

- Heater
- Supports

- Insulating Bead

- Vacuum
- Bulb

- Basic Thermoelement

- Iin

- Pout

- Current Measurements

- Thermoelement

- Precision Shunt

- Vin

- Vout

- Thermoelement

- Precision Resistor

- Driven Shield

- Voltage Measurements

## Ac-dc Standards

- MJTC Primary Standards
- Group of 10 MJTCs
- Different construction
- Different manufacturers
- Different eras
- Used for both voltage and current
- Used from 2 V to 10 V, 2.5 mA to 25 mA,
- 	40 Hz to 10 kHz
- Intercompare to < 0.4 μV/V
- Primary standard uncertainty: 0.5 μV/V

**Robustness!**

## Temperature Gradients

- Single-junction thermal converter
- Working temperature:
- ≈ 200 oC above ambient

- Large thermal gradients
- Significant thermoelectric errors

- Multijunction thermal converter
- Working temperature:
- ≈ 50 oC above ambient

- Small thermal gradients
- Reduced thermoelectic errors

## Ac-dc Standards

- Voltage Converters
- Reference standards
- Coaxial thermal converters
- Special converters for frequency extensions
- Working standards
- Coaxial thermal converters

- Current Converters
- Reference standards
- High-current thermoelements
- Working Standards
- High current thermoelements
- High current shunts

## Voltage Build-up and Build-down

**Primary**
**Standards**

- 10 Hz

- 100 Hz

- 1 kHz

- 10 kHz

- 100 kHz

- 1 MHz

- 1 kV

- 100 V

- 10 V

- 1 V

- 0.2 V

- Build-up

- Build-down

**Voltage**

**Frequency**

- Frequency
- Extension

- Frequency
- Extension

## Voltage Parameter Space

**1000 V**

**100 V**

**10 V**

**1 V**

**100 mV**

**10 mV**

**1 mV**

**10 Hz**

**100 Hz**

**1 kHz**

**10 kHz**

**100 kHz**

**1 MHz**

**10 MHz**

**100 MHz**

**1 GHz**

- < 5

- < 1

- < 10

- < 20

- < 50

- < 300

- < 300

- < 8000

- < 4000

## Current Parameter Space

- 100 mA

- 100 μA

- 1 mA

- 10 mA

- 1 A

- 10 A

- 100 A

- 200 μA/A

- 100 μA/A

- 20 μA/A

- 30
- μA/A

- 30 μA/A

- 50 μA/A

- 70
- μA/A

- 40 μA/A

- 50 μA/A

- 100 μA/A

- 120 μA/A

- 300 μA/A

- 400 μA/A

- 500 μA/A

- 1 Hz

- 10 Hz

- 100 Hz

- 1 kHz

- 10 kHz

- 100 kHz

- Expanded Parameter Space