Low Frequency Military Immunity Test: CS101 and

Challenges & Pitfalls

Soydan ÇAKIR

TUBITAK UME, Gebze, Kocaeli, Turkey

05/09/2019

EMC Europe 2019, Barcelona

CS101, Conducted Susceptibility, Power Leads 30 Hz – 150 kHz

• Frequency Range: 30 Hz (Second Harmonic of EUT power frequency) – 150 kHz

• Dwell Time: The greater of 3 seconds or EUT response time per frequency

• Frequency Step: max 5%

• Unit: Voltage (dBuV)

• Modulation: None

• Application: Power leads (not including returns)

Purpose: The CS101 test is applied to military and aerospace equipment by injecting low frequency sinusoidal voltage ripples to power ports of EUT between 30 Hz and 150 kHz in order to determine susceptibility levels of EUT

General Test Setup for Military Tests

Test Setup for Table Top Equipment Test Setup for Floor Standing Equipment

MIL-STD461F : Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems And Equipment

CS101 Calibration CS101 Test

CS101 Testing

CS101 Test Setup for DC and Single-Phase AC EUT

CS101 Test Setup for Three-Phase EUT (3-phase delta)

CS101 Test Setup for Three-Phase EUT (3-phase wye)

Challenge/Pitfall 1: No Just-Before-Test Verification in Standard

Pitfall: Many laboratories perform calibration by means of a simple scope but use AC power frequency filters, special ripple detectors or FFT-based software solutions in the test to cancel AC power frequency. As there is no proposed just-before-test verification under power frequency in CS101 testing, problems with used filters&connections&software cannot be detected before the test, which may lead to wrong testing.

EUT power frequency filters & special detectors are used in test to cancel the power frequency but there is no verification before test for test setup

AC Power Frequency

Filters & Att.

Simple scope is used in calibration

Proposed Just-Before-Test Verification

EUT Power frequency filters are placed and AC power is activated !!!! Following this, calibration power is played back !!!

AC Power ON

!!!!

No AC

Power

Step 2: Test on 200 ohm by playing back the calibration power Step 1: Calibration on Test Setup using 200 ohm

Calibration on the test setup with 200 ohm without AC power by using # Curve 1

S. Cakir., M. Ozturk, O. Sen, C.B. Tektas, S. Acak, M. Cetintas, “MIL STD 461F CS101 Testing and Power Frequency Cancelation", 7th Asia Pasific International Symposium on Electromagnetic Compatibility, Shenzhen (18-21/05/2016) : 3 p.

Conclusions 1

An effective just-before-test verification is introduced to verify the CS101 test system including used filter solutions, which prevents wrong testing.

The proposed verification method does not only verify used filter solutions but also verify the entire measurement chain from the voltage measurement point to the software screen.

The standard should include a CS101 verification method like CS114.

Challenge/Pitfall 2: Power AC Frequency and CS101 Ripples at the same place

Challenge: The levels of CS101 voltage ripples which are injected into the EUT must be continuously measured by using an oscilloscope under the AC power frequency of the EUT because the power level injected into the EUT or the ripple voltage level induced across the EUT input, whichever reaches its limit first, must limit the test leveling as per the standard.

EUT AC power frequency & CS101 voltage ripples at the same place !!!

State-of-the-Art Filter Solutions

Diagram of Passive Filter* Photo of Passive Filter

Designed Active Filter Connected to Passive Filter

*https://www.evaluationengineering.co

m/conducted-susceptibility-

testing.php-2

* S.Cakir, M.Ozturk, O.Sen, B.Tektas, S.Acak,

M.Cetintas , “MIL STD 46IF CS101 testing and

power frequency cancelation”, Asia-Pacific

International Symposium on Electromagnetic

Compatibility (APEMC), 17-21 May 2016

Verification of Hardware Filters

220 VAC, 50 Hz No Mains

Time Domain Solution

We employed the “Welch” function to calculate the estimate of the power spectrum

Online:https://www.ofcom.org.

uk/__data/assets/pdf_file/0019/40348/timedomainemc.pdf

Welch, P, “The Use of Fast Fourier Transform for the Estimation of Power Spectra: A Method Based on Time Averaging Over Short, Modified Periodograms”, IEEE Transactions on Audio and

Electroacoustics, Vol. AU-15, No. 2, pages 70-73, 1967.

S.Cakir, M.Ozturk, C.B.Tektas, O.Sen, S.Acak, M.Pous, "FFT-Based Time Domain Solution to Power Frequency Issue of CS101 Testing for Military and Aerospace Equipment", 2018 Joint IEEE EMC & APEMC Symposium, Singapore (14-17/05/2018)

Validation Setup for Time Domain Solution

Calibration on Test Setup (No AC power !!!)

Test Setup (with AC power and with

FFT-based solution !!!)

Time Domain Solution - Scope Snapshots

220 VAC, 50 Hz 115 VAC, 400 Hz

440 VAC, 50 Hz 190 VAC, 60 Hz

Time Domain Solution Validation

220 VAC, 50 Hz 115 VAC, 400 Hz

440 VAC, 50 Hz 190 VAC, 60 Hz

Conclusions 2

An effective FFT-based time domain solution to the major issue which is always encountered in CS101 tests of AC / DC military or aerospace equipment is introduced.

The introduced method excellently separates the CS101 voltage ripples from the AC power frequency even in the highest power supply voltages such as 440VAC

It is significantly more precise with an average deviation of 0.4 dB in comparison to hardware filter solutions with an average deviation of up to 5 dB

It provides good ease of use in comparison to filter solutions as it only requires simple connection of an oscilloscope probe across the EUT regardless of the value of AC power frequency without using cumbersome filters and complex or specific setup arrangements.

Power estimate calculation during each leveling step slightly slows down CS101 testing in comparison to the regular RMS reading used with hardware filter solutions.

Challenge/Pitfall 3: Undesired Voltage across Mains

Challenge: The ripple voltage injected to the EUT shall not drop across the power source side and all the ripple energy shall be routed to the EUT otherwise it may cause undertesting ! This must be verified during the testing as per MIL-STD461G!

EUT AC power frequency & low frequency voltage ripples at the same place

Ripple voltage shall not drop here !

EUT AC power frequency & voltage ripples at the same place!

Definition of the Problem

New measurement method for Power Source Side Ripple Voltage in CS101 Testing

The ripple voltage that drops across the power source side is simultaneously measured together with the EUT ripple voltage by means of the concurrent use of two scope probes and by using FFT-based time domain solution.

S.Cakir, O.Sen, M.Ozturk, "Investigation of Ripple Voltage Across Capacitor in Military CS101 Test by Using FFT-Based Time Domain Solution", 2018 IEEE Symposium on Electromagnetic Compatibility Signal & Power Integrity, Long Beach (30/07-03/08/2018)

Power Source Side Ripple Voltage Verification Results for EUT: Load

(a) with chamber filter (b) without chamber filter

(c) extra 10 µF capacitor at the power source side

Conclusions 3

An effective FFT-based time domain solution in order to measure the CS101 ripple voltage that unintentionally drops across the power source under the AC power frequency was proposed.

The proposed method easily detects undertesting and also helps with the solution.

Challenge/Pitfall 4 :No Clear Injection Point In Standard

The exact position of the injection point over a 2 m cable is not clear in the standard !

Pitfall: There is no specific definition of the injection point in the standard apart from a simple general diagram shown below. On the other hand, influence of the injection point and the decoupling capacitor position over a 2 m cable may reach significant levels especially beyond 30 kHz.

Investigation on Influence of Injection Point on Test Results

The capacitor is in the vicinity of the LISNs whereas the coupling transformer is close to the EUT

Both of the capacitor and the coupling transformer are in the vicinity of the EUT

Both of the capacitor and the coupling transformer are in the vicinity of the LISNs

The Setup 4 is a sequel to the Setup 3 to measure the voltage across the EUT

Setup 1 Setup 2

Setup 3 Setup 4

Influence of Injection Point on Test Results

Desired ripple voltage values measured across EUT side:

Undesired ripple voltage values measured across source side:

S. Cakir, O. Sen, M. Ozturk, M. Celep, "Influence of Injection Point Selection on Military Low Frequency Immunity Test Results", 2019 ESA Workshop on Aerospace, Budapest (20-22/05/2019) : 5 p.

Conclusions 4

The effect of the positions of the coupling transformer and 10 µF decoupling capacitor on test results was demonstrated. The setup, in which the coupling transformer and 10 µF capacitor are placed in the vicinity of the EUT (Setup 2), is the most effective and efficient in terms of the minimum loss on the cable and the maximum energy injected into the EUT.

The standard should define the injection point clearly like CS114, CS115 and CS116 tests

Setup 2

Ongoing Discussions on CS101 Testing

When the EUT voltage limit is not achieved across the EUT in the test stage, how is calibration power applied? In order to limit test power, should we return to ; - Signal generator calibration settings? (commonly used one)

- Amplifier output calibration voltage?

- Calibration power by multiplication of voltage & current ?

- The lesser of calibration power or calibration current ?