How it Works
Cirrus Logic
Loading...
AN365
User Manual
14 pgs654.63 Kb0
Table of contents
Loading...

Cirrus Logic AN365 User Manual

Download
A
v(t)
i(t)
R
Figure 1. Rogowski Coil Current Sensor
AN365
Application Note
Using the CS5480/84/90 Energy Measurement IC
with Rogowski Coil Current Sensors

1. Introduction

This application note presents accuracy results from testing the CS5480 with three different types of Rogowski coil sensor. The CS5484 and CS5490 use the same core technology. Testing results of the CS5484 and CS5490 show nearly identical results. Comparable power meters were constructed using the CS5480 and three Rogowski coils: Pulse Electronics PA3202NL, TAEHWATRANS TR9L, and Sentec Mobius. Accuracy test results are presented that demonstrate that the CS5480 can achieve an energy measurement accuracy of 0.1% over a 4000:1 dynamic range when interfaced to a Rogowski coil.

2. Rogowski Coil Overview

A Rogowski coil current sensor is a helical coil of wire wrapped around an AC line conductor and used to measure the flow of electric charge through the conductor. Since a Rogowski coil has an air core instead of an iron core, the measurements show excellent linearity with practically no saturation problems. In addition, the Rogowski coil rates highly for electrical isolation from the buss bar, and is light weight with low material cost. The Rogowski coil is increasingly being implemented when measuring high-current AC power and energy.
Cirrus Logic, Inc.
http://www.cirrus.com
Copyright Cirrus Logic, Inc. 2012
(All Rights Reserved)
MAR’12
AN365REV1
AN365
vt
AN
0
–
l
------------------


di t
dt
-----------


=
[Eq. 1]
V kI=
[Eq. 2]
The voltage v(t) that is induced in the Rogowski coil is proportional to the rate of the charge of current (di(t)/dt) and is based on Faraday's law. The voltage v(t) produced by a Rogowski coil is calculated using Equation 1:
where,
A = Area of each small loop
N = Number of turns l=2R and is the length of the winding
µ
= Permeability of free space
0
When the AC line current, I, is a 50Hz or 60 Hz sinusoidal, Equation 1 can be simplified to Equation 2.
where
k = Sensitivity constant that represents the output voltage per ampere at 50Hz or 60Hz.
Most Rogowski coil manufacturers provide a sensitivity constant for the coil. See Table 1:
Model Manufacturer Output Voltage/Ampere at 50Hz
PA3201NL Pulse 416µV/A
TR9L Taehwatrans 1.7mV / A
Mobius Sentec 80µ V / A
Table 1. Rogowski Coil Parameters

3. Rogowski Coil Support

Since the output of a Rogowski coil is proportional to the derivative of the instantaneous primary current, an integrator is required to retrieve the original current signal. The CS5480 incorporates selectable digital integrators for both current channels. The integrators have the frequency responses illustrated in Figure 2 to compensate for the 90 degree phase shift and 20dB /decade gain generated by the Rogowski coil.
2 AN365REV1
AN365
10
0
10
1
10
2
10
3
-90
-80
-70
-60
-50
-40
-30
Frequency (Hz)
Phase (degrees)
Phase of Rogowski Integrator
10
0
10
1
10
2
10
3
0
10
20
30
40
50
60
Frequency (Hz)
Magnitude (dB)
Magnitude of Rogowski Integrator
Figure 2. Frequency Response of the Digital Integrator
CS5480
IIN 1-
IIN 1+
27nF
27nF
27nF
27nF
V+
V-
GND
GND
IIN1-
IIN1+
J1
Rogowski Coil
PA 3202 NL
Current
1kΩ100Ω
1kΩ100Ω
Figure 3. Typical Connections Between a Rogowski Coil and the CS5480

3.1 Connection Between a Rogowski Coil and the CS5480

Since the Rogowski coil has an inherent 20dB/decade gain, a single-pole low-pass RC anti-aliasing filter is not capable of attenuating the high-frequency noise. Two cascaded low-pass RC filters are required to produce a
40dB/decade attenuation at high frequency. Figure 3 illustrates the typical connections between a Rogowski
coil sensor and the CS5480. If the Rogowski coil has a shielding lead, it should be connected to ground.
AN365REV1 3
AN365

3.2 PGA Selection on the Current Channel

The CS5480 current channel incorporates a programmable gain amplifier (PGA) with two selectable input gains. The Config0 register bits I1PGA[1:0] select either 10x or 50x gain for the current channel. The two PGA settings dictate the maximum input voltage that can be applied to the IIN± inputs.
CS5480 I-channel PGA Maximum Input Voltage
10x
50x
Table 2. PGA Settings
167mV
35mV
RMS
RMS
The Rogowski coil output voltage produced with the maximum AC line current (I
) should not exceed the max-
max
imum input voltages listed in Table 2. Some margin should be considered according design requirements.

3.3 Filter Selection

The CS5480 high-pass filter (HPF) and integrator are set using the Config2 register. To support a Rogowski coil, HPF must be enabled on the voltage channel and the integrator must be enabled on the current channel.

3.4 Calibration and Compensation

To compensate for the tolerances and variations in components and to remove the residual offset and noise in the system, a gain calibration, phase compensation, AC offset calibration, and power offset correction should be performed. For more information, see the CS5480 data sheet, entitled Three Channel Energy Measurement IC, for details regarding the calibration and compensations process.

4. Measurement Accuracy Results with Rogowski Coils

The CS5480 load performance (measurement accuracy under different load conditions) has been tested with three different types of Rogowski coil. The active and reactive energy load performance is tested with a single energy pulse. The meter constant is set at 2000 impulses per kWh, or 2000 impulses per kVarh. The I is calculated based on CS5480 I U
= 240V and line frequency of 50Hz.
n
register values. All of the tests were conducted at room temperature and with
RMS
load performance
RMS
4 AN365REV1

4.1 Load Performance with Rogowski Coil PA3202NL

-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.01 0.1 1 10 100
Percentage Error (%)
Load Current (A)
PF = 1 Lagging PF = 0.5 Leading PF = 0.5
Figure 4. Active Energy Load Performance

4.1.1 Active Energy Load Performance

AN365
Power Factor Load Current (A) Current Dynamic Range (x:1) Error
80 1 0.04%
8 10 0.04%
0.8 100 0.04%
PF = 1
0.16 500 0.04%
0.08 1000 0.07%
0.04 2000 0.05%
0.03 3333 0.06%
0.02 4000 0.02% 80 1 0.05%
Lagging PF = 0.5
8 10 0.05%
0.8 100 0.04%
0.16 500 0.06%
0.08 1000 0.05%
0.04 2000 0.06% 80 1 0.04%
Leading PF = 0.5
8 10 0.04%
0.8 100 0.05%
0.16 500 0.04%
0.08 1000 0.05%
0.04 2000 0.07%
Table 3. Active Energy Load Performance
AN365REV1 5

4.1.2 Reactive Energy Load Performance

-1
-0.5
0
0.5
1
0.01 0.1 1 10 100
Percentage Error (%)
Load Current (A)
sin ࢥ = 1 Lagging sin ࢥ = 0.5 Leading sin ࢥ = 0.5
Figure 5. Reactive Energy Load Performance
AN365
Power Factor Load Current (A) Current Dynamic Range (x:1) Error
80 1 0.00%
8 10 0.01%
0.8 100 0.01%
sin = 1
0.16 500 -0.02%
0.08 1000 -0.02%
0.04 2000 -0.01%
0.03 3333 0.00%
0.02 4000 -0.03% 80 1 0.23%
8 10 0.24%
Lagging sin = 0.5
0.8 100 0.17%
0.16 500 0.21%
0.08 1000 0.16%
0.04 2000 0.22% 80 1 -0.20%
8 10 -0.20%
Leading sin = 0.5
0.8 100 -0.26%
0.16 500 -0.23%
0.08 1000 -0.25%
0.04 2000 -0.24%
Table 4. Reactive Energy Load Performance
6 AN365REV1
AN365
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.1 1 10 100
Percentage Error (%)
Load Current (A)
Figure 6. I
RMS
Load Performance
4.1.3 I
Load Performance
RMS
Register Value
I
RMS
(10-Second Average)
Load Current (A)
Current Dynamic
Range (x:1)
80 1 0.60011034 0.02%
8 10 0.060009873 0.02%
0.8 100 0.006001252 0.02%
0.16 500 0.001200491 0.04%
0.08 1000 0.000600857 0.14%
Table 5. I
Load Performance
RMS
I
RMS
Error
AN365REV1 7

4.2 Load Performance with Rogowski Coil TR9L

-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.01 0.1 1 10 100
Percentage Error (%)
Load Current (A)
PF = 1 Lagging PF = 0.5 Leading PF = 0.5
Figure 7. Active Energy Load Performance

4.2.1 Active Energy Load Performance

AN365
Power Factor Load Current (A) Current Dynamic Range (x:1) Error
120 1 0.01%
60 2 0.04% 12 10 0.06%
1.2 100 0.02%
PF = 1
0.24 500 0.01%
0.12 1000 0.00%
0.06 2000 -0.02%
0.036 3333 0.00%
0.03 4000 0.02%
120 1 0.05%
60 2 0.04% 12 10 0.03%
Lagging PF = 0.5
1.2 100 -0.06%
0.24 500 0.05%
0.12 1000 0.01%
0.06 2000 -0.01%
120 1 0.01%
60 2 -0.02%
Leading PF = 0.5
12 10 -0.03%
1.2 100 -0.03%
0.06 2000 -0.09%
Table 6. Active Energy Load Performance
8 AN365REV1

4.2.2 Reactive Energy Load Performance

-1
-0.5
0
0.5
1
0.01 0.1 1 10 100
Percentage Error (%)
Load Current (A)
sin ࢥ = 1 Lagging sin ࢥ = 0.5 Leading sin ࢥ = 0.5
Figure 8. Reactive Energy Load Performance
AN365
Power Factor Load Current (A) Current Dynamic Range (x:1) Error
120 1 -0.01%
12 10 -0.03%
1.2 100 -0.04%
sin = 1
0.24 500 -0.05%
0.12 1000 -0.04%
0.06 2000 0.06%
0.036 3333 0.02%
0.03 4000 0.01% 120 1 0.17%
12 10 0.24%
1.2 100 0.14%
0.24 500 0.10%
Lagging sin = 0.5
0.12 1000 0.07%
0.06 2000 0.07% 120 1 -0.20%
Leading sin = 0.5
12 10 0.24%
1.2 100 -0.22%
0.24 500 -0.22%
0.12 1000 -0.22%
0.06 2000 -0.21%
Table 7. Reactive Energy Load Performance
AN365REV1 9
AN365
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.1 1 10 100
Percentage Error (%)
Load Current (A)
Figure 9. I
RMS
Load Performance
4.2.3 I
Load Performance
RMS
Register Value
I
RMS
(10-Second Average)
I
RMS
Error
Load Current (A)
Current Dynamic
Range (x:1)
120 1 0.599961683 -0.01%
60 2 0.299958968 -0.01%
12 10 0.059990853 -0.02%
1.2 100 0.005999583 -0.01%
0.24 500 0.001200372 0.03%
0.12 1000 0.000600344 0.06%
Table 8. I
Load Performance
RMS
10 AN365REV1

4.3 Load Performance with Sentec

-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.01 0.1 1 10 100
Percentage Error
Load Current (A)
Leading PF = 0.5Lagging PF = 0.5
PF = 1
Figure 10. Active Energy Load Performance

4.3.1 Active Energy Load Performance

AN365
Power Factor Load Current (A) Current Dynamic Range (x:1) Error
120 1 0.02%
60 2 0.02% 12 10 0.02%
1.2 100 0.02%
PF = 1
0.24 500 0.02%
0.12 1000 0.03%
0.06 2000 0.03%
0.036 3333 0.06%
0.03 4000 -0.07% 120 1 0.02%
60 2 0.02% 12 10 0.01%
Lagging PF = 0.5
1.2 100 0.01%
0.24 500 0.03%
0.12 1000 0.02%
0.06 2000 0.01% 120 1 0.02%
60 2 0.03% 12 10 0.01%
Leading PF = 0.5
1.2 100 0.00%
0.24 500 0.01%
0.12 1000 -0.01%
0.06 2000 0.00%
Table 9. Active Energy Load Performance
AN365REV1 11

4.3.2 Reactive Energy Load Performance

-1
-0.5
0
0.5
1
0.01 0.1 1 10 100
Percentage Error (%)
Load Current (A)
sin ࢥ = 1 Lagging sin ࢥ = 0.5 Leading sin ࢥ = 0.5
AN365
Figure 11. Reactive Energy Load Performance
Power Factor Load Current (A) Current Dynamic Range (x:1) Error
120 1 -0.02%
60 2 -0.02% 12 10 -0.03%
1.2 100 -0.03%
sin = 1
0.24 500 0.03%
0.12 1000 0.01%
0.06 2000 0.02%
0.036 3333 0.09%
0.03 4000 0.08% 120 1 0.19%
Lagging = 0.5
60 2 0.19% 12 10 0.19%
1.2 100 0.17%
0.24 500 0.20%
0.12 1000 0.26%
0.06 2000 0.23% 120 1 -0.23%
60 2 -0.22% 12 10 -0.24%
Leading = 0.5
1.2 100 -0.24%
0.24 500 -0.2%
0.12 1000 -0.16%
0.06 2000 -0.17%
Table 10. Reactive Energy Load Performance
12 AN365REV1
AN365
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.1 1 10 100
Percentage Error (%)
Load Current (A)
4.3.3 I
Load Performance
RMS
Figure 12. I
Load Performance
RMS
Register Value
I
RMS
(10-Second Average)
I
RMS
Error
Load Current (A)
Current Dynamic
Range (x:1)
120 1 0.599985965 0.00%
60 2 0.300011613 0.00%
12 10 0.06000053 0.00%
1.2 100 0.006000024 0.00%
0.24 500 0.001199722 -0.02%
0.12 1000 0.000600541 0.09%
Tab le 11 . I
Load Performance
RMS

5. Summary

The CS5480 energy measurement IC supports Rogowski coils using digital integrators. With the exception of two single-pole RC filters, no other external components are required. With on-chip digital calibration and compensation algorithms, the CS5480 can achieve 0.1% energy measurement accuracy over 4000:1 dynamic range.
AN365REV1 13
Revision History
Contacting Cirrus Logic Support
For all product questions and inquiries contact a Cirrus Logic Sales Representative. To find one nearest you go to http://www.cirrus.com
IMPORTANT NOTICE
Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable. However, the information is subject to change without notice and is provided "AS IS" without warranty of any kind (express or implied). Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those pertaining to warranty, indemnification, and limitation of liability. No responsibility is assumed by Cirrus for the use of this information, including use of this information as the basis for manufacture or sale of any items, or for infringement of patents or other rights of third parties. This document is the property of Cirrus and by furnishing this information, Cirrus grants no license, express or implied under any patents, mask work rights, copyrights, trademarks, trade secrets or other intellectual property rights. Cirrus owns the copyrights associated with the information contained herein and gives con­sent for copies to be made of the information only for use within your organization with respect to Cirrus integrated circuits or other products of Cirrus. This consent does not extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROP­ERTY OR ENVIRONMENTAL DAMAGE ("CRITICAL APPLICATIONS"). CIRRUS PRODUCTS ARE NOT DESIGNED, AUTHORIZED OR WARRANTED FOR USE IN PRODUCTS SURGICALLY IMPLANTED INTO THE BODY, AUTOMOTIVE SAFETY OR SECURITY DEVICES, LIFE SUPPORT PRODUCTS OR OTHER CRIT­ICAL APPLICATIONS. INCLUSION OF CIRRUS PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER'S RISK AND CIRRUS DISCLAIMS AND MAKES NO WARRANTY, EXPRESS, STATUTORY OR IMPLIED, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR PARTICULAR PURPOSE, WITH REGARD TO ANY CIRRUS PRODUCT THAT IS USED IN SUCH A MANNER. IF THE CUSTOMER OR CUSTOMER'S CUSTOMER USES OR PERMITS THE USE OF CIRRUS PRODUCTS IN CRITICAL APPLICATIONS, CUSTOMER AGREES, BY SUCH USE, TO FULLY INDEMNIFY CIRRUS, ITS OFFICERS, DIRECTORS, EMPLOYEES, DISTRIBUTORS AND OTHER AGENTS FROM ANY AND ALL LIABILITY, INCLUD­ING ATTORNEYS' FEES AND COSTS, THAT MAY RESULT FROM OR ARISE IN CONNECTION WITH THESE USES.
Cirrus Logic, Cirrus, the Cirrus Logic logo designs, EXL Core, and the EXL Core logo design are trademarks of Cirrus Logic, Inc. All other brand and product names in this document may be trademarks or service marks of their respective owners.
Revision Date Changes
REV1 MAR 2012 Initial Release.
AN365
14 AN365REV1
Loading...
Buy Points How it Works FAQ Contact Us Questions and Suggestions Privacy Policy Cookie Policy Terms of Use