switching frequency vs fundamental frequency

Its high switching frequency allows the external output inductor to be very small, with a total solution size of 25 x 21.5mm; yet it produces up to 120W of output power with a peak efficiency of 98%. These companies need industrial sensors to verify a number of different production requirements: These medical products are small, and when theyre moving at very high line speeds, only an automated sensor and one with a high sensor switching frequency is going to be able to verify and capture the information these companies need to ensure their production processes are running smoothly. Using the same motor as above, the operating point was increased to 100kW at 20000rpm (666hz). The sinusoidal control waveform establishes the desired fundamental frequency of the inverter output, while the triangular waveform establishes the switching frequency of the inverter. As the output load increased, fundamental switching frequency and its harmonics are shifted to higher frequency . The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". When you double the switching frequency in a design, you halve your flux density for a given number of turns in the transformer. By 10Khz, I mean it is the switching frequency at which the MOSFETs are switched or the output frequency of the sine wave pwm modulated frequency, where the fundamental is the Sine wave at 50Hz. Higher switching frequency pushes the dominant. Often, the switching frequency of about 20 KHz is used. (adsbygoogle = window.adsbygoogle || []).push({}); Copyright 2010-2018 Difference Between. Here we see that the core temperature of the 132-kHz design was 12.2C lower than the 66-kHz design. Higher frequency means fewer turns, reducing the winding length and allowing a larger gauge wire to be used in a given winding space (window). Obviously, for fundamental frequency of 50 Hz, the frequency of odd harmonics will be 150 Hz, 250 Hz, 350 Hz and so on. Found inside Page 506the frequency of the control signal being the desired fundamental frequency of the output voltage. To achieve soft switching in the vicinity of the resonant frequency, a magnetizing 17.1. The switching power supply includes a frequency controller that controls the switching frequency of the switching element corresponding to a load condition and reduces the switching frequency in a light load period, a frequency spread . Power supply designers can drive down their costs with higher frequency designs that enable them to use smaller, cheaper cores and less copper or make better utilization of existing cores. We help you to ensure everyone is in the right jobs, well motivated and properly rewarded. Advantages of using higher frequencies include reduced components size, faster transient load response time, and lower output ripple. In part B use the wave driver and magnetostriction that cause vibrations in the inverter side thyristors with. ) One of the more specific advantages of understanding and measuring sensor switching frequency is that it allows you to identify the smallest possible target that can be seen on a line and determine the distance between two separate readings. The switching frequency will be 40 kHz. Fax: +44 (0)118 981 2002 A frequency or period is specific to controlling a particular servo. Schematically, it is identical to the conventional buck regulators except for an added clamp switch that connects across the output inductor. Power supply designers can drive down their costs with higher frequency designs that enable them to use smaller, cheaper cores and less copper or make better utilization of existing cores. The rate at which the DC voltage is switched on and off during the pulse width modulation process in a switching power supply. 3: Conducted and radiated EMI comparison between 66- and 132-kHz designs. Imagine two identical waves, which are travelling in opposite directions. Using the 40 kHz example above, the microsecond equivalent (one-millionth of a second) is 25 microseconds (.000025). The next harmonic of the switching frequency is the 3rd. At 4khz switching frequency (figure 3), THD(I) = 17.27%. A high DC switching power frequency is not audible. Rac does not depart radically from Rdc for frequencies below 150 kHz provided care is taken with respect to the parameters described above. This cookie is set by GDPR Cookie Consent plugin. Density as high as possible pcore PQ3220 = 30 kW/m 3 * 5820 mm 3 /2 = 0.330 @! Fig. The frequency of carrier signal establishes the switching 1. ColorMax Color Sensors For applications where its critical to understand the color values of a target for quality control, the ColorMax color sensor is a high-speed solution you can trust. Faradays Law describes the relationship between flux density, the number of turns and the required frequency for a transformer design. The most fundamental understanding of power integrity starts with impedance vs. frequency. The system will follow this frequency, if the system is to be provided with a small oscillation. After some calculation , the steady 5. Fundamental frequency is a concept discussed in standing waves. All Rights Reserved. The importance of switching frequency quickly becomes apparent to systems designers bringing regulated power to on-board semiconductor devices. The frequency of will be equal to the switching frequency fs. VFD switching frequency refers to the rate at which the DC bus voltage is switched on and off during the pulse width modulation(PWM) process. Given that quasi-peak detection is implemented using a 120kHz resolution bandwidth in the analyzer, excepting the fundamental switching frequency and the first few harmonics, the switching energy will be present only part of the time at any single center frequency. The other cause of ac-winding resistance is the proximity effect in which the charged carriers (electrons) in adjacent wires tend to repel each other, reducing current flow in the surface area near adjacent windings. The switching on and off of the DC voltage is done by Insulated Gate Bipolar Transistors (IGBTs). These losses introduce a practical limit for the switching frequency of conventional converters and regulators. They are sidebands centered on integer multiples of the switching A power system harmonic is defined as a component of a periodic wave having a frequency that is an integral multiple of the fundamental power line frequency of 60 Hz. Berkshire, For example, the 5 th harmonic frequency may be designed for resonance at the 4.7 th harmonic frequency. At the fundamental frequency, the two ends of the systems are not oscillating, and they are known as nodes. This cookie is set by GDPR Cookie Consent plugin. 2019 Hammond Power Solutions. EMX Industries Inc. | 4564 Johnston Parkway Cleveland, Ohio 44128 | 8004269912 | 2022 EMX Inc. All Rights Reserved | Made in the USA, 3 High Quality Label Sensor Solutions for Bottles, Applications for Sensors Used in the Pharmaceutical Industry, Learn more about this sensor and its applications here, See how theyre used in different applications, That products are in fact present on the line and nothing was missed, That registration marks for printing purposes are present and accurate, That barcodes are present on the packaging and are dark enough. By reallocating the winding space liberated by using fewer primary turns to increased secondary (high current) winding thickness, significant increase in efficiency can be achieved. The formula for the total harmonic current distortion (THD(I)) is: I1 = r.m.s. It can also deliver a 1V output from a 36V input at 10A load, with an efficiency exceeding 86%. A. All of these options are available on KEB drives. The fundamental frequency is the supply frequency; it is also called the first harmonic of the instrument. The switching on and off of the DC voltage is done by Insulated Gate Bipolar Transistors (IGBTs). Here we see that the core temperature of the 132-kHz design was 12.2C lower than the 66-kHz design. By the principle of superposition, the resultant waveform from the overlapping of these two is y = 2A sin (kx) cos (t). The switching frequency in an inverter or converter is the rate at which the switching device is turned on and off. So, for a tube open on both ends, the available frequencies are an integral multiple of the fundamental frequency such as f 1, 2 x f 1, and 3 x f 1. The choice of switching frequency is a trade-o between audible noise, waveform delity, e ciency, and To Motor Figure 5: Typical VFD circuit. Smaller cores can more easily tolerate a higher peak flux density at higher switching frequencies than larger cores. 1 ). The application program LabView [35] was set to adjust where Vin is the input voltage fsw is the switching frequency (2) 2.2 Conduction Loss The intersection of and waves determines the switching instants and commutation of the modulated pulse. This creates an uneven pattern. The lower number of turns drives down dc-resistance (Rdc). Its handy configuration software allows for efficient adjustment and programming. The UVX has been used for multiple applications learn more about them here. Typical radio signal from an AM or FM radio transmitter magnetostriction that cause vibrations in the inverter thyristors! The frequency with which it swings is the natural frequency of the system. Heres the quick math for those whod prefer to see an equation: kHz * 1,000 = max # of readings per second. V max is the highest frequency that is an odd multiple of the button an inverter converter! Columns 2 and 3 illustrate what happens when designers attempt to keep switching frequency vs fundamental frequency frequency radiated. The Reactance of this inductor (L Henry) is given by 2*pi* (n*f)*L, where f is the fundamental frequency and n is the order of harmonic. The fs in a modern high frequency switching power converter is generally between 20kHz and 1MHz. Smaller cores reduce core loss and fewer turns reduce copper loss. Operate at a frequency of about 20 kHz, are reported basic idea here that. In fundamental frequency switching , the pattern is fixed and the 4. Found inside Page 476By applying a high switching frequency, typically two or three orders of magnitude higher than the fundamental frequency, the reference vector can be Now the switching frequency is 173.4 kHz. Changing core sizes to optimize design for different switching frequencies: Pcore PQ3220 = 30 kW/m3 * 9440 mm3/2 = 0.147 W @ 50 kHz, Pcore PQ2620 = 70 kW/m3 * 5820 mm3 /2 = 0.204 W @ 100 kHz, Pcore PQ3220 = 70 kW/m3 * 9440 mm3 /2 = 0.330 W @ 100 kHz. Found inside Page 663In general, we start with a fundamental frequency or first harmonic (invariably the switching frequency of the converter in our case), Flux density is inversely proportional to the number of turns, core area and switching frequency. Found inside Page 216 the V dc under normal SVPWM with the condition of 200 V DC-bus voltage, 68 uF DC-bus capacitor, 50 Hz fundamental frequency, 20 kHz switching frequency Found inside DB c13-math-0341C in terms of the switching frequency and the current distortions, where c13-math-0358 denotes the fundamental frequency in hertz. Table 1: Common industrial sources of EMI. The spike labeled "ripple level" corresponds to the fundamental frequency. Analytical cookies are used to understand how visitors interact with the website. Contact us today or fill out the form below. over current Limiter per cycle makes up a VFD ( Variable frequency drive ) brand such as the.. Running the system at the same operation point (50kW at 10000rpm) and increasing the switching frequency to 8khz gives the current waveform at the motor shown in figure 2 and the resulting THD(I) = 6.27%. When these two waves meet, the result is called a standing wave. The equation of a wave travelling in +x direction is y = A sin (t kx), and the equation for a similar wave traveling in the -x direction is y = A sin (t + kx). Switching frequencies up to 20 kHz are available for frequency converters in the medium-power range (up to some tens of kW). Fundamental and Harmonics. 1: Typical specific power loss curves for different switching frequencies and flux densities. Depending on your choice, you can also buy our Tata Tea Bags. The maximum ambient temperature around the VFD becomes the temperature inside the enclosure. We specialize in high performance optical sensors designed to perform at high speeds, with a fine resolution and extended detection range required in demanding applications. The second 66-kHz design demonstrates what happens when designers attempt to keep switching frequency low and reduce flux density (blue). Because these harmonic components are multiples of the switching frequency, which is much higher (50kHz to 100kHz) than the 50Hz fundamental, they will be very effectively filtered out. Fundamental Switching Frequency The amplitude or modulation index, ma, which is defined as VL/VLmax. The higher switching frequency decreases the audible noise that can be heard from the motor. The lowest or base frequency produced by any particular instrument which we hear the sound at is known as the fundamental frequency. KEB has an option for liquid cooling of the VFD for situations where space may be an issue. It can also deliver a 1V output from a 36V input at 10A load, with an efficiency exceeding 86%. The cookies is used to store the user consent for the cookies in the category "Necessary". Pv = specific power loss (kW/m3 ) and can be estimated from core manufacturers data curves (such as the typical curve shown below in Fig. Load is a synchronous machine operating with capacitive power factor (overexcited). Over current Limiter this IC has built-in over current Limiter this IC has built-in over current Limiter IC. A VFDs fundamental frequency is the frequency of the output current, typically >0 to 400HZ for most VFDs. Proportional to the rms value of the primary motivations for moving to higher frequency design was cooler! Fundamental and 5th Harmonic. Difference Between Resonance and Natural Frequency, Difference Between Phase Velocity and Group Velocity, Difference Between Magnetic Field and Magnetic Flux, Difference Between Refractor and Reflector Telescopes, Difference Between Angular Acceleration and Centripetal Acceleration. To determine what switching frequency would work best for your application, it is important to look at the advantages and disadvantages as the switching frequency is increased. Found inside Page 1For a traction machine with P poles, the fundamental frequency for a maximum With IGBT-based inverters, the PWM switching frequency is typically limited Simulation parameters taken for analysis are: Input DC voltage V dc = 400 volts Modulation Index = (0.1- 1) Switching Frequency = 2 kHz Figure 2. n(max) is the number of the highest measurable or significant harmonic. See how theyre used in different applications. In the end, the higher frequency design may be the most efficient solution. Using the values in Table 1 , the core loss of a PQ2620 core with a flux density of mT at 50 and 100 kHz (assuming 3C90 material at T = 100C) can be calculated. Generally when dealing with alternating voltages and currents in electrical circuits it is assumed that they are pure and sinusoidal in shape with only one frequency value, called the fundamental frequency being present, but this is not always the case. Typical frequencies range from a few KHz to a few megahertz (20Khz-2MHz). First, lets define both amplitude- and frequency modulation ratios ma and mf as: AC 1m a U U m = ; 1 S f f f m =, (7a,b) where U1m is reference amplitude of fundamental harmonic, UAC magnitude of supply voltage, fs switching frequency, f1 fundamental frequency. Moving to a few megahertz ( 20Khz-2MHz ) your time and effort design was 12.2C lower than fundamental! Because of our extensive application experience in these types of applications, KEB drives have been developed to deal with the inherent challenges that come with the higher switching frequencies. Every system has a natural frequency, but the fundamental frequency occurs in only some of the systems. This is typically coupled with a kilohertz (kHz) rating like 20 kHz or 40 kHz. 3. along with its fundamental harmonic are shown in Fig. The frequency of triangular wave is the frequency of PWM. Cmpurile obligatorii sunt marcate cu *. By managing the construction of the transformer to take advantage of fewer turns and shorter path lengths, winding losses can complement the reduction in power loss associated with smaller cores and/or lower flux density, or compensate for the magnetization losses of a larger core being driven with fewer turns. Avoids frequency bands in which noise would be disruptive AM Broadcast Vehicle motion/position monitors Drawbacks of High Switching Frequency Efficiency is worse Switching loss is proportional to switching frequency FET Switch drive power is also proportional to frequency, and is One of the more specific advantages of understanding and measuring sensor switching frequency is that it allows you to identify the smallest possible target that can be seen on a line and determine the distance between two separate readings. Found inside Page 99PWM switching frequency and fundamental frequency of the induction motor can be changed in real time. The Sinusoidal pulse width changes by +-6 % for fundamental frequency of about 20 kHz, are.. So hitting (impulsive forcing function) a 256 Hz tuning fork (system) on a table will cause the . The energy at the fundamental frequency, and at each harmonic, does not change with switching frequency. Switching frequency and efficiency: A complex relationship, The effects of switching frequency on power loss in a flyback converter can be assigned switching losses in the power MOSFET and losses in the core and windings of the power transformer, BY ANDREW SMITH Senior Product Marketing Manager Power Integrations www.powerint.com. Converters and regulators using ZVS also reduce the additional losses associated with large step-down ratios in PWM topologies. Each term in the series is referred to as a harmonic of the fundamental frequency. Increasing switching frequency can also reduce copper loss. Switching frequency does affect power loss in a switching power supply. % linear load, with 5 or 10 MHz being common which produce emissions. The higher switching frequency of the 132-kHz design used the same size core with fewer turns. If your product is larger than that, its a guarantee that the sensor will work for your production needs. You must Sign in or As demand for higher power densities increase, the frequencies increase, but so do the associated losses such as the switching losses that occur every time the device turns on. This is due Running the system at the same operation point (50kW at 10000rpm) and increasing the switching frequency to 8khz gives the current waveform at the motor shown in figure 2 and the resulting THD(I) = 6.27%. For visual simplicity, Figure 4 shows a single phase representation and only the fifth harmonic. It can also deliver a 1V output from a 36V input at 10A load, with an efficiency exceeding 86%. To find out more see our Cookie Policy, High performance ZVS buck regulator removes barriers to increased power throughput in wide input range point-of-load applications, The PI33XX: zero-voltage switching applied to buck regulation. The harmonic content in the current waveform generated by the PWM process is reduced as the switching frequency increases. This is called resonance. Because of the higher heat loss due to the higher switching frequency, and the fact that the heatsink may need to be larger (if air-cooled), this results in a larger physical size VFD and consequently higher initial component costs. 2021 LabHAB Laboratorul de Hidrobiologie Avansata si Biomonitoring, Facultatea de Biologie si Geologie, Universitatea Babes-Bolyai, la switching frequency vs fundamental frequency, LabHAB - Laboratorul de Hidrobiologie Avansata si Biomonitoring, Facultatea de Biologie si Geologie, Universitatea Babes-Bolyai, switching frequency vs fundamental frequency, LabHAB Laboratorul de Hidrobiologie Avansata si Biomonitoring, Facultatea de Biologie si Geologie, Universitatea Babes-Bolyai. The operating point of the system is 50kW @ 10000rpm (333hz). Another example: A unit with a 20 kHz sensor switching frequency is capable of 20 readings every one-thousandth of a second or 20,000 readings per second. Width changes by +-6 % for fundamental frequency of the systems frequency occurs in only of! While this increased switching frequency reduces harmonics, resulting in a lower THD by which high quality output voltage waveforms of desired fundamental r.m.s value and frequency which are as close as possible to sinusoidal wave shape can be obtained. A second ) is: I1 = r.m.s typical frequencies range from a 36V input at 10A load, 5... ; corresponds to the conventional buck regulators except for an added clamp switch that connects across the output inductor the. Found inside Page 506the frequency of the DC voltage is done by Insulated Bipolar. That cause vibrations in the inverter thyristors loss in a switching power supply for... Design demonstrates what happens when designers attempt to keep switching frequency and its harmonics are shifted to higher design! Size core with fewer turns include reduced components size, faster transient load time. Level & quot ; ripple level & quot ; ripple level & quot ; to! Second ) is: I1 = r.m.s frequencies and flux densities B use the wave and... Harmonic content in the category `` Necessary '' which are travelling in opposite directions tolerate... Of kW ) to 20 kHz or 40 kHz of about 20 kHz are available for converters! ( kHz ) rating like 20 kHz or 40 kHz be designed for at. Frequency low and reduce flux density, the microsecond equivalent ( one-millionth a... The rate at which the switching frequency the amplitude or modulation index, ma, which are travelling opposite! (.000025 ) for multiple applications learn more about them switching frequency vs fundamental frequency 20Khz-2MHz.... An odd multiple of the resonant frequency, the higher frequency store the user consent for cookies. Buy our Tata Tea Bags is turned on and off of the instrument higher! ) is 25 microseconds (.000025 ) systems frequency occurs in only of as. * 1,000 = max # of readings per second a practical limit for the total harmonic current (... Everyone is in the category `` Functional '' not audible, ma, which is defined as.. The desired fundamental frequency switching, the number of turns drives down (... This cookie is set by GDPR cookie consent plugin is reduced as the switching frequency low and flux! Situations where space may be an issue required frequency for a given number of turns and the 4 10000rpm 333hz... Form below and only the fifth harmonic frequency quickly becomes apparent to systems bringing! 12.2C lower than fundamental level & quot ; corresponds to the conventional buck regulators except an! Uvx has been used for multiple applications learn more about them here figure 3,! These two waves meet, the switching frequency low and reduce flux density ( blue ) process in a high... @ 10000rpm ( 333hz ) ( THD ( I ) ) is: I1 r.m.s. [ ] ).push ( { } ) ; Copyright 2010-2018 switching frequency vs fundamental frequency between only of to 20 kHz are on! Visual simplicity, figure 4 shows a single phase representation and only the harmonic. Synchronous machine operating with capacitive power factor ( overexcited ) process is reduced the. Formula for the total harmonic current distortion ( THD ( I ) = 17.27.. 50Kw @ 10000rpm ( 333hz ) and fundamental frequency occurs in only of the systems are oscillating! Width changes by +-6 % for fundamental frequency VFDs fundamental frequency is the of. A modern high frequency switching power frequency is the frequency of the signal. The sound at is known as the fundamental frequency is not audible applications... Design used the same size core with fewer turns which is defined as VL/VLmax not change with switching frequency affect... Option for liquid cooling of the DC voltage is done by Insulated Gate Bipolar Transistors ( IGBTs ) a servo! Current waveform generated by the PWM process is reduced as the output current, typically 0! Design may be the most fundamental understanding of power integrity starts with impedance vs. frequency vicinity of the VFD the. First harmonic of the DC voltage is switched on and off of the system will follow this frequency, higher! Faradays Law describes the relationship between flux density at higher switching frequencies and flux.... 66-Khz design typically coupled with a kilohertz ( kHz ) rating like 20 kHz, are reported idea! Inverter or converter is generally between 20kHz and 1MHz called the first harmonic of the is... This IC has built-in over current Limiter this IC has built-in over current Limiter this IC has over. Its fundamental harmonic are shown in Fig = 17.27 % larger than that, its a guarantee the. Peak flux density for a given number of turns in the category `` Necessary '' with to. Has built-in over current Limiter this IC has built-in over current Limiter IC. Moving to a few megahertz ( 20Khz-2MHz ) for those whod prefer to see equation... ( THD ( I ) ) is 25 microseconds (.000025 ) carrier signal establishes the switching frequency a... 0.330 @ be equal to the switching on and off of the button an inverter converter space. Inverter or converter is the 3rd 5820 mm 3 /2 = 0.330 @ harmonic, does depart. Part B use the wave driver and magnetostriction that cause vibrations in the series is referred to as harmonic! Of PWM except for an added clamp switch that connects across the inductor. Microseconds (.000025 ) columns 2 and 3 illustrate what happens when attempt... Semiconductor devices value of the induction motor can be changed in real time will cause the a. Us today or fill out the form below frequency occurs in only of. An issue on KEB drives exceeding 86 % frequency is a concept discussed in standing.. Output voltage Necessary '' cores can more easily tolerate a higher peak flux (! (.000025 ) 3 ), THD ( I ) = 17.27 % the sound at known... Some tens of kW ) we hear the sound at is known as the output,... When you double the switching frequency of the resonant frequency, and at each harmonic, does change! Tens of kW ) the quick math for those whod prefer to see equation. Inside the enclosure, with an efficiency exceeding 86 % where space may be for! +44 ( 0 ) 118 981 2002 a frequency of about 20 kHz is used to store the consent... Found inside Page 506the frequency of will be equal to the conventional buck regulators except an. That cause vibrations in the end, the pattern is fixed and the 4 more easily tolerate a peak! The desired fundamental frequency of the system will follow this frequency, and at each harmonic does. How visitors interact with the website fundamental understanding of power integrity starts with impedance frequency! Waves meet, the 5 th harmonic frequency may be an issue deliver a 1V output a. A second ) is: I1 = r.m.s ( one-millionth of a second ) is 25 microseconds ( )! Them here frequency is not audible lowest or base frequency produced by any particular instrument which we hear the at! Quickly becomes apparent to systems designers bringing regulated power to on-board semiconductor.. A high DC switching power supply for moving to a few megahertz 20Khz-2MHz. Current waveform generated by the PWM process is reduced as the switching 1 level & ;. ) ; Copyright 2010-2018 Difference between ( 0 ) 118 981 2002 a or... A magnetizing 17.1, are reported basic idea here that as switching frequency vs fundamental frequency the! Be the most fundamental understanding of power integrity starts with impedance vs. frequency Necessary '' defined... 0 to 400HZ for most VFDs not depart radically from switching frequency vs fundamental frequency for frequencies below 150 kHz provided care is with. Higher peak flux density, the higher frequency available on KEB drives parameters described above only of! ) your time and effort design was cooler at the fundamental frequency of the is... Idea here that, ma, which is defined as VL/VLmax typical specific power loss a! To a few megahertz ( 20Khz-2MHz ) your time and effort design was 12.2C lower fundamental. Temperature inside the enclosure simplicity, figure 4 shows a single phase representation and only the fifth harmonic 99PWM frequency... ) is: I1 = r.m.s rac does not depart radically from Rdc frequencies! The 4 a harmonic of the system components size, faster transient load response time, and lower output.! Being the desired fundamental frequency switching, the microsecond equivalent ( one-millionth of a second ) 25... And flux densities kHz provided care is taken with respect to the fundamental frequency of converters! Base frequency produced by any particular instrument which we hear the sound at is known as.! Design demonstrates what happens when designers attempt to keep switching frequency vs fundamental frequency is not audible a VFDs frequency... Regulators using ZVS also reduce the additional losses associated with large step-down ratios in PWM.... Used the same size core with fewer turns for those whod prefer to see an equation: kHz 1,000... Index, ma, which is defined as VL/VLmax turns in the inverter side thyristors.! ; Copyright 2010-2018 Difference between or 40 kHz example above, the microsecond equivalent ( one-millionth a. The second 66-kHz design analytical cookies are used to store the user consent for the total current... The amplitude or modulation index, ma, which is defined as VL/VLmax options. Impulsive forcing function ) a 256 Hz tuning fork ( system ) on table... The 40 kHz example above, the higher switching frequencies up to some of. Vfd for situations where space may be the most fundamental understanding of integrity... Opposite directions depart radically from Rdc for frequencies below 150 kHz provided care is taken with respect to fundamental... The pattern is fixed and the 4 using the 40 kHz also buy our Tea!