High-precision Heat/Cold Meter Reference Design

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heat meter
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This reference design provides a high-precision differential temperature measurement (DTM) subsystem for heat and cold meters in residential and industrial applications.

TI’s reference design (TIDA-01526) implements a single chip, cost-effective DTM system that can be combined with TI’s ultra-sonic or rotation detection flow measurement subsystems to provide a full heat or cold meter solution.

The design implements a high-precision differential temperature measurement (DTM) subsystem using a 24-bit, low-power, delta-sigma ADC. Heat and cold meter DTM subsystems typically use two 2- or 4-wire Resistance Temperature Detectors (RTD) such as PT100, PT500, or PT1000 and can achieve a differential temperature measurement accuracy of 10 mK over a water temperature range of 3°C to 180°C.

Features

  • Meets EN1434 requirements for RTD sensor pair temperature measurement subsystems in heat and cold meters and heat calculators
  • Max. 60 mK absolute temperature deviation from 0 to 150°C for 2- or 4-wire RTDs meets ±100 mK limit (EN1434-5:2014)
  • Meets max. ±700 mK error limit for each PT sensor at 3 typical temperature measurements points, e.g. at 10°C, 30°C and 50°C (EN1434-5:2014)
  • ADC122x04 achieves ultra-low power consumption by power-cycling with 50-μs start-up time and programmable current source, gain, and output data rates
  • Differential temperature measurement of two RTDs in series with 0.01°C resolution
  • 40-pin BoosterPack form factor (BoosterPack 20-pin backwards compatible)

System Description

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The European EN1434-1 through EN1434-6 set of standards define the technical requirements for heat meters in the European Union (EU); such devices are mandatory in many EU countries to bill for heat in multi-dwelling units.

Heat meters are flow meters (usually with water) with an integrated high-precision DTM subsystem, which enables calculating the heat (or cold in cooling systems) based upon the flow volume and the temperature differential between forward (outlet) and backward (inlet) flow.

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Residential heat meters use 2-wire PT500 or PT1000 sensors, which are firmly integrated (soldered) inside the device and cannot be replaced in the field. 4-wire RTDs are more often for use in heat calculators, which are separate units, processing the input data from separate flow and temperature sensors. In heat calculators, the temperature sensors can be detached from the primary systems and mounted up to 15 m (2-wire RTDs) or farther away (4-wire RTDs required). The RTD sensors of the same precision class—for example Class A as in EN 60751—or the heat calculator device itself can be replaced independently from each other. This reference design has been tested in both 2-wire RTD and 4-wire RTD configurations.

Applications

• Residential and Industrial Heat Meters With 2- or 4-Wire PT100/PT500/PT1000
• Heat Calculators (Units Detached From Flow and Temperature Sensors)
• Industrial Cold Meters (Measures Cold Instead of Heat)
• High-Precision Differential Temperature Measurements With PT100/PT500/PT1000

Click here for the reference design.

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