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AN2167: DescriptionUsing the STPM01 with a shunt current sensor; File Size44KB，5 Pages; ManufacturerSTMicroelectronics; Websitehttp://www.st.com/

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Using the STPM01 with a shunt current sensor

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AN2167

Application note

Using the STPM01 with a shunt current sensor

Introduction

This document describes how a shunt current sensor can be used with the STPM01

metering device in single-phase metering applications without tamper detection.

Special considerations must be taken into account when the shunt is designed:

■

The current density must be kept constant

The power dissipation must be reduced, as it can influence the ambient temperature

within the meter housing. In the event of large current overloads, this can become an

explosion hazard.

Note:

Special safety precautions must be followed while the meter is connected to the power line

and opened. The ground plane of the meter is at a high voltage level because the shunt has

to measure the current flow through a hot conductor without any galvanic isolation. This is a

safety hazard for the operators and can destroy the connected equipment.

For more information on the STPM01, refer to the full datasheet.

October 2008

Rev 2

1/5

www.st.com

AN2167

Examples of sensor shunt usage in energy meters

2.1

Examples of sensor shunt usage in energy meters

Single-phase application without tamper

A shunt measures the current flow through the hot conductor of the line, so pin F becomes

the local ground of the meter and the larger resistor of the voltage divider is connected to pin

N of the meter. The voltage divider drop must be connected to the anti-aliasing filter input for

the voltage channel of the STPM01. Both voltage pins of the shunt should be connected to

the anti-aliasing filter input for the primary current channel of the STPM01, while the

secondary current channel may be connected to local ground.

All of the connections to the anti-aliasing filter inputs should be implemented with the

shortest wires possible, and with the smallest area of loop possible (without any other signal

in the vicinity), formed by the following:

●

source impedance element

both wires

input impedance of the filter

The STPM01 device should be configured with PST = 3 and ADDG = 1 (settings for the

shunt current sensor, current amplification factor 32, and no tamper detection).

This type of metering application can operate as a standalone with a stepper display or a

microcontroller may be implemented in order to access more measured results in the

STPM01 using the LCD, automatic meter reading (AMR), or tariffing functions.

2.2

Single-phase application with tamper

It is not possible to connect two shunts to the STPM01 because one would generate its

output at the high voltage level. Therefore, a current sensor with integral galvanic isolation

must be used for the primary current channel, while another shunt is used for the secondary

channel or vice-versa.

Although a shunt produces an output voltage which is proportional to the primary current

like a current transformer (CT) does, it is difficult to combine a CT with a shunt in single

phase metering applications with tamper detection due to differences in phase error

indicators and output voltage levels. These differences must be resolved with components

outside of the STPM01.

2.3

Multi-phase application with or without tamper

It would be cost-prohibitive to use three or four shunts with three or four STPM01 devices,

plus the necessary three galvanic isolations and additional power supplies, as well as a

microcontroller to achieve the objectives of a three-phase meter design. The other problem

would be the excessive levels of power dissipation produced by three shunts operating at

maximum phase currents.

3/5

AN2167

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5/5

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