Shimmer 3 Manual de usuario

Realtime Technologies Ltd IMU User Manual

ECG User Guide

Revision 1.12

Realtime Technologies Ltd ECG User Guide

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Realtime Technologies Ltd ECG User Guide

Table of Contents

1. Introduction.............................................................................................................................. 4

2. General Information ................................................................................................................. 5

2.1. Safety Information ............................................................................................................. 5

2.2. Pre-Requisites.................................................................................................................... 5

2.3. ECG Unit Specification Overview ........................................................................................ 5

3. Using the ECG Unit .................................................................................................................... 6

3.1. Basic System Overview....................................................................................................... 6

3.2. ECG Leads .......................................................................................................................... 7

Electrode Positioning................................................................................................................. 7

Wilson's Central Terminal .......................................................................................................... 9

3.3. Configuration Options and Recommended Settings............................................................ 9

Data Rate................................................................................................................................. 10

Gain......................................................................................................................................... 10

Input Multiplexer..................................................................................................................... 11

Right-Leg Drive ........................................................................................................................ 11

Test Signal ............................................................................................................................... 12

Respiration demodulation ....................................................................................................... 12

Lead-off detection configuration.............................................................................................. 12

4. Measuring ECG Signals ............................................................................................................ 14

4.1. Best Practice on How to Acquire a High Quality ECG signal............................................... 14

Skin Preparation ...................................................................................................................... 14

Sampling Frequency................................................................................................................. 14

Wires....................................................................................................................................... 14

Filtering ................................................................................................................................... 14

4.2. Basic ECG Waveform Features.......................................................................................... 15

4.3. How to Determine the Heart Rate from ECG .................................................................... 15

Example HR Calculation ........................................................................................................... 16

Overview of Popular QRS Detection Methods .......................................................................... 17

4.4. Aliasing Error and Sampling Rate...................................................................................... 18

4.5. Signal Calibration ............................................................................................................. 19

ADC Offset Measurement ........................................................................................................ 20

Realtime Technologies Ltd ECG User Guide

Gain Measurement.................................................................................................................. 20

5. Hardware Considerations........................................................................................................ 20

5.1. Board Layout.................................................................................................................... 20

5.2. Channel assignment......................................................................................................... 22

5.3. Data considerations ......................................................................................................... 23

6. Firmware Considerations ........................................................................................................ 23

7. Troubleshooting...................................................................................................................... 23

7.1. Verifying That Your ECG Unit Works ................................................................................. 23

7.2. Signal Quality ................................................................................................................... 23

8. References .............................................................................................................................. 24

9. Appendices ............................................................................................................................. 25

9.1. Legacy Hardware.............................................................................................................. 25

Board Layout ........................................................................................................................... 25

Channel assignment................................................................................................................. 26

Trouble shooting...................................................................................................................... 26

9.2. Opening the Shimmer3 expansion enclosure.................................................................... 27

Realtime Technologies Ltd ECG User Guide

1. Introduction

This document is an accompaniment to the Shimmer3 ECG Unit (called ECG Unit in the rest of this

document). Its purpose is to aid the user in getting started with ECG measurements.

The ECG Unit can be configured to measure electrical signals from the skin, including ECG

(Electrocardiograph). Any user who wishes to use Shimmer hardware to record EMG

(Electromyograph) signals from the skin should refer to the Shimmer3 EMG User Guide, which is

available for download from http://www.shimmersensing.com.

The five-wire, four-lead ECG Unit can be configured to record the pathway of electrical impulses

through the heart muscle. This data can be recorded on resting and ambulatory subjects, or during

exercise to provide information about the heart’s response to physical exertion. Signals are collected

from the skin via five wires, which are connected externally to the ECG Unit, and to which should be

attached conventional disposable electrodes. The ECGUnit uses a low-power, multichannel analog

front-end especially designed for biopotential measurements, consisting of delta-sigma analog-to-

digital converters and programmable gain amplifiers.

Realtime Technologies Ltd ECG User Guide

2. General Information

2.1. Safety Information

As a precaution it is important to note that the ECG leads are not to be applied to the subject's body

while unit is in a USB dock or multi-charger.

2.2. Pre-Requisites

A Shimmer3 ECG Unit programmed with appropriate firmware. For example, LogAndStream

(v0.7.0 or greater) can be used to stream data over Bluetooth and/or log data to the SD card

or SDLog (v0.13.0 or greater) can be used to log data to the SD card; both are available for

download from www.shimmersensing.com.

Five DIN snap leads.

-9-inch and 18-inch leads are shipped with the ECG Development Kit and ECG

Bundles.

-Replacements can be purchased from www.shimmersensing.com.

Surface ECG electrodes.

-Disposable electrodes are shipped with the ECG Development Kit and ECG Bundles.

-For replacements, see www.shimmersensing.com. Alternatively, the Covidien

Kendall Disposable Surface EMG/ECG/EKG electrodes 1" (24mm) or Covidien Kendall

Disposable Surface EMG/ECG/EKG electrodes 1 3/8" (35mm), available on www.bio-

medical.com with product codes 'BRD H124SG' and 'BRD H135SG', respectively, and

the Ambu Blue Sensor T electrodes, available from various suppliers, are all suitable

options and have been validated for use with Shimmer equipment.

2.3. ECG Unit Specification Overview

For specifications on the general Shimmer3 part (i.e. microprocessor, radio, data storage and

inertial sensors) of the Shimmer3 ECG Unit, please refer to the Shimmer User Manual.

Gain: Configurable (1, 2, 3, 4, 6, 8, 12)

Data rate: software configurable (125, 250, 500, 1000, 2000, 4000, 8000 SPS)

Input differential dynamic range

: approx 800 mV (for gain = 6).

Bandwidth

: 8.4 kHz

Ground: Wilson Type Driven Ground

Input Protection: ESD and RF/EMI filtering; Current limiting; inputs include defibrillation

protection (survive only, not repeat). NOTE: For inputs LA and RA the defibrillation

protection is not present in order to facilitate Respiration demodulation.

Connections: Input RA, Input LA, Input LL, Input Vx, Reference (RL)

oAll Hospital-Grade 1mm Touchproof IEC/EN 60601-1 DIN42802 jacks.

Ultra-lightweight (31 grams); Compact Dimensions (65 x 32 x 12 mm).

EEPROM memory: 2048 bytes.

Calculated specification; exact value subject to environmental and component variation. ADS1292R is

optimized for power with a differential input signal of approx. 300 mV when gain = 6.

Specifications from ADS1292R datasheet; exact value subject to environmental and component variation.

Realtime Technologies Ltd ECG User Guide

3. Using the ECG Unit

3.1. Basic System Overview

Figure 3-1: Simplified Block Diagram

Electrodes: Each ECG board connects to RA (white), LA (black), RL (green), LL (red) and Vx

(brown) electrodes.

Defibrillation protection: Survive only; not repeat. No defibrillation protection is present for

inputs RA and LA to facilitate Respiration demodulation.

EMI Filter: Reduces electromagnetic interference; -3dB filter bandwidth is approximately

3MHz.

Right-Leg Drive Amplifier (RLD Amp): Counteracts common-mode interference (e.g. from

mains power lines, fluorescent lights and other sources).

Programmable Gain Amplifier (PGA): Increases amplitude of input signal; seven gain

settings available. See Section 4.5 to accurately calculate the gain of your device. Default

gain is configurable in software.

 Analog to Digital Converters ( ADC): Converts the input analogue signals to a digital

representation of this signal by a 24-bit signed integer value to each sample. These values

are fed to the Shimmer3 processor to be saved to the SD card or transmitted over Bluetooth.

Realtime Technologies Ltd ECG User Guide

3.2. ECG Leads

In the context of electrocardiography, the word "lead" is used to refer to the signal of the voltage

difference between two electrodes (i.e. the signal produced by the ECG recorder). In order to avoid

any confusion, the wires that are used to physically connect the electrodes to the ECG Unit are

referred to throughout this document as just that - "wires".

The ECG Unit provides a four-lead ECG solution, with the following leads being measured in the

recommended configuration:

Bipolar limb leads:

oLead I (LA-RA) is the ECG vector signal measured from the RA (right arm) position to

the LA (left arm) position. This is output on the ExG1 Ch2 channel of the ECG Unit.

oLead II (LL-RA) is the ECG vector signal measured from the RA (right arm) position to

the LL (left leg) position. This is output on the ExG1 Ch1 channel of the ECG Unit.

oLead III (LL-LA) is the ECG vector signal measured from the LA (left arm) position to

the LL (left leg) position. This is derived by subtracting Lead I from Lead II.

Unipolar leads:

oVx-WCT is the ECG vector signal measured from the Wilson's Central Terminal (WCT)

voltage to the Vx position

. For more information on the WCT voltage, see the

description below. This is output on the ExG2 Ch2channel of the ECG Unit.

Electrode Positioning

The inputs to the ECG Unit are labelled according to the suggested placement, in order to measure

the four channels listed above:

Bipolar limb lead electrodes:

oLA Left Arm

oRA Right Arm

oLL Left Leg

oRL Right Leg

Unipolar lead electrode positions:

oVx V1, V2, V3, V4, V5or V6, on the chest

Any of the unipolar Vx leads (i.e. V1, V2, V3, V4, V5and V6) can be measured on the ExG2 Ch2 channel by

positioning the electrode at the Vx input with the appropriate placement on the body.

Realtime Technologies Ltd ECG User Guide

Figure 3-2 Example positioning of the electrodes for ECG measurement with 18″ leads

Figure 3-3: Example positioning of the electrodes for ECG measurement with 9” leads

Figure 3-2 shows an example of how the electrodes should be positioned on the body. The

electrodes for the bipolar limb leads (LA, RA, LL and RL) are represented by green nodes and wires,

whilst the V1, V2, V3, V4, V5and V6positions for the unipolar leads, are represented by brown nodes

and wires.

Although it is common practise to place the limb electrodes on the arms/legs, according to their

names, in reality, all of the limb electrodes can be placed on the chest. The important thing is that

Realtime Technologies Ltd ECG User Guide

each electrode should be placed on the body, away from the heart and in the direction of the joint

to the relevant limb. For example, the RA electrode can be placed anywhere on the chest as long as

it is positioned away from the heart in the direction of the right shoulder, as shown in Figure 3-3.

The reference electrode (RL) can be placed anywhere on the body as long as it is outside of the

triangle formed by the 3 other limb electrodes (i.e. RA, LA and LL). In the diagram below it is placed

at the V5position, laterally on the left side of the torso. This position allows for the highest quality

capturing of R waves. [1]

The Vx electrode can be placed at any of the positions, V1, V2, V3, V4, V5or V6, depending on the

user's requirements.

Wilson's Central Terminal

The Wilson's Central Terminal (WCT) is a voltage that represents the average potential of the body

and acts as a reference point, with respect to which the voltage difference for the unipolar leads is

measured. It is calculated by averaging the voltage measured at the RA, LA and LL electrodes.

The inverted WCT voltage is driven to the body via the RL electrode to create a negative feedback

loop in the measurement system and provide common mode interference rejection.

3.3. Configuration Options and Recommended Settings

The ECG Unit contains two ADS1292R chips from Texas Instruments; these have a very wide and

varied range of available configuration options. These chips are referred to as "Chip1" and "Chip2"

throughout this document. This section aims to provide recommended settings, which will suit the

needs of most ECG measurement applications. The experienced user who wishes to have full control

over all of the configuration settings should refer to the ADS1292R datasheet from Texas

Instruments for more details.

There are two ADS1292R chips on the ECG Unit and each of these chips has eleven bytes of

configurable register settings. Ten of these configurable bytes are listed in Table 3-1 and their

recommended values are discussed in this section. The final byte, which pertains to GPIO settings, is

dealt with in firmware and not discussed here.

Byte

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

CONFIG1:

Configuration Register 1

Data Rate

(DR2, DR1, DR0)

CONFIG2:

Configuration Register 2

INT_T

EST

TEST_F

REQ

LOFF:

Lead-Off Control Register

CH1SET:

Channel 1 Settings

Gain1

(G1_2, G1_1, G1_0)

MUX1

(M1_3, M1_2, M1_1, M1_0)

CH2SET:

Channel 2 Settings

Gain2

(G2_2, G2_1, G2_0)

MUX2

(M2_3, M2_2, M2_1, M2_0)

RLD_SENS:

Right Leg Drive Sense Selection

PDB_RL

RLD_LO

FF_SENS

RLD Settings

(RLD2N, RLD2P, RLD1N, RLD1P)

The Bit 3 in CONFIG2 denotes “X=0” for SR47-1 revision, and “X=1” for SR47-4 and greater revisions. This

feature has been configured automatically in both LogAndStream 0.11.0 and SDLog_v0.19.0 (and newer).

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