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Lake Shore Model 330 Autotuning Temperature Controller User’s Manual

Service & Calibration

5-5

5.6 TOP OF ENCLOSURE REMOVE AND REPLACE PROCEDURE
WARNING: To avoid potentially lethal shocks, turn off controller and disconnect it from AC power line

before performing this procedure. Only qualified personnel should perform this procedure.

REMOVE TOP

Turn off the controller and disconnect the line cord from rear of controller.

Use Phillips screwdriver to remove 6 screws; 3 on top of each side of the controller.

Slide the top up and off.

REPLACE TOP

Replace the top enclosure.

Use Phillips screwdriver to replace 6 screws; 3 on top of each side of the controller.

Reconnect power cord to rear of controller and set power switch to on.

5.7 OPERATING SOFTWARE EPROM AND PRECISION OPTION NOVRAM REPLACEMENT

The operating software for the Model 330 is contained on two Erasable Programmable Read Only Memory

(EPROM) Integrated Circuits (ICs). The reference designator for the master EPROM is U11 (DC.HEX) and the

slave is U16 (SV.HEX). The optional Precision Option is provided on a Non-Volatile Ram Access Memory

(NOVRAM) IC. See Figure 5-9 for locations of these ICs. Use the procedure below to replace either one or

both existing software EPROMs or the NOVRAM.

CAUTION: The EPROM and NOVRAM are Electrostatic Discharge Sensitive (ESDS) devices. Wear

shock-proof wrist straps (resistor limited to <5 mA) to prevent injury to service personnel and to avoid

inducing an Electrostatic Discharge (ESD) into the device.

Follow the REMOVE TOP procedure in Paragraph 5.6.

Locate master software EPROM U11 (DC.HEX), slave EPROM U16 (SV.HEX), or Precision Option

NOVRAM (U12) on the main circuit board. Note orientation of existing IC. See Figure 5-9.

Use IC puller to remove existing EPROM(s)/NOVRAM from socket.

Note orientation of new EPROM(s)/NOVRAM. Use IC insertion tool to place new device(s) into socket.

XX HEX

DATE

Typical EPROM

Match notch on

EPROM to notch

in socket

Typical NOVRAM

DALLAS

xxxxxxxxx

Match notch on

NOVRAM to

notch in socket

Follow the REPLACE TOP procedure in Paragraph 5.6.

Proceed to Paragraph 2.12 and follow the power up sequence.

Содержание 330

Страница 1: ...Shore Cryotronics Inc No government or other contractual support or relationship whatsoever has existed which in any way affects or mitigates proprietary rights of Lake Shore Cryotronics Inc in these...

Страница 2: ...sibility of errors exists In any important research as when using any laboratory equipment results should be carefully examined and rechecked before final conclusions are drawn Neither Lake Shore nor...

Страница 3: ...kle Blvd Westerville OH 43082 8888 USA hereby declare that the equipment specified conforms to the following Directives and Standards Application of Council directives 73 23 EEC 89 336 EEC Standard to...

Страница 4: ...installation and operating instructions in the User s Manual are followed there should be no degradation in EMC performance Pay special attention to instrument cabling Improperly installed cabling may...

Страница 5: ...put Settings 2 3 2 5 Grounding and Shielding 2 3 2 6 Sensor Installation 2 4 2 6 1 Diode Model 330 1X and Platinum Model 330 2X Connections 2 4 2 6 1 1 Two Lead Versus Four Lead Measurements 2 4 2 6 1...

Страница 6: ...13 3 4 4 Instrument Reset and Factory Default Settings 3 13 3 4 5 Power Up PUP Configuration 3 14 3 5 Thermocouple Controller Operation Model 330 4X Only 3 15 3 5 1 Sensor Attachment 3 15 3 5 2 Therm...

Страница 7: ...Rating 5 1 5 3 Rear Panel Connector Definitions 5 2 5 4 IEEE 488 Interface Connector 5 3 5 5 Optional Serial Interface Cable and Adapters 5 4 5 6 Top of Enclosure Remove and Replace Procedure 5 5 5 7...

Страница 8: ...ls 5 3 5 6 Model 2001 RJ 11 Cable Assembly Wiring Details 5 4 5 7 Model 2003 RJ 11 to DE 9 Adapter Wiring Details 5 4 5 8 Model 2002 RJ 11 to DB 25 Adapter Wiring Details 5 4 5 9 Typical Model 330 PCB...

Страница 9: ...es Control Control Stability to 2 5 mK Three Term PID Control Loop 25 or 50 Watt Maximum with 2 lower power ranges in decade steps Setpoint Ramping Interface 4 5 Digit LED Display for High Visibility...

Страница 10: ...nhance Model 330 thermometry accuracy with a Lake Shore calibrated sensor and 8000 Series Precision Calibration Option or with SoftCal Model 330 control software compares the measured control sensor v...

Страница 11: ...at 30 K 0 5 mK at 4 2 K 30 mK at 4 2 K Equivalence 21 mK at 77 K 12 mK at 77 K 72 mK at 77 K 22 mK at 300 K 16 mK at 300 K 13 mK at 300 K 32 mK at 300 K 18 mK at 475 K 15 mK at 800 K Sensor Units Dis...

Страница 12: ...Setpoint P I D and Heater Range Heater Output Type Variable DC Current Source Heater Setting Resolution 15 bits Max Power To Heater 50 Watts 25 Watts Field Configurable Heater Current by Range High 1...

Страница 13: ...ms where step responses are less than 5 seconds where there are few measured points correct determination of the PID parameters is difficult Manually select gain and reset rate is not normally require...

Страница 14: ...contact or induced by an electrostatic field The low energy source that most commonly destroys Electrostatic Discharge Sensitive ESDS devices is the human body which generates and retains static elec...

Страница 15: ...c they are dangerous because they replace air in a normal breathing atmosphere Liquid helium is an even greater threat because a small amount of liquid evaporates to create a large amount of gas Store...

Страница 16: ...nd The instrument is equipped with a three conductor AC power cable Plug the power cable into an approved three contact electrical outlet or use a three contact adapter with the grounding wire green f...

Страница 17: ...erials If there is freight damage to the instrument file proper claims promptly with the carrier and insurance company and notify Lake Shore Notify Lake Shore immediately of any missing parts Lake Sho...

Страница 18: ...The assembly consists of the power line jack the power switch and the fuse holder The line cord plugs into the power line jack The power switch turns the unit on and off The fuse holder contains a 2 A...

Страница 19: ...Millivolts DIP Switch S1 is for Channel A and S2 is for Channel B If the internal DIP switches are improperly set the display will read Er when the Input Type Input Type key is pressed The normal fron...

Страница 20: ...voltage sensing pair that cause measurement error In two lead measurement the leads that measure sensor voltage are also current carrying leads The voltage measured at the instrument is the sum of the...

Страница 21: ...element and leads make all thermal contact to the sensor through the base A thin braze joint around the sides of the SD package electrically connects to the sensing element Avoid contact to the sides...

Страница 22: ...ils 2 6 2 Thermocouple Model 330 4X Connections The thermocouple input has a thermal block to connect thermocouple wires The positive and negative terminals correspond to V and V and should match the...

Страница 23: ...Sensitivity at 20 K 4 6 V K Chromel CuFe 0 15 The Chromel Copper Iron thermocouple consists of a Ni Cr alloy Chromel as the positive thermoelement and a Copper 0 15 Iron alloy as the negative thermoe...

Страница 24: ...tion numbers 11 thru 31 as a User Curve See Table 2 3 and Paragraph 3 2 7 to use SoftCal 2 8 PRECISION CALIBRATION OPTION There are three Model 330 precision options The Model 8000 Precision Calibrati...

Страница 25: ...re ND 30 to connect to the heater Do not run heater leads coincident with the sensor leads due to potential capacitive pick up between the two sets of leads If heater leads must be close to sensor lea...

Страница 26: ...default PUP condition If left on the instrument powers up in the same configuration it powered down Off indicates power up memory updates are disabled and the instrument powers up in the same configur...

Страница 27: ...ature units in kelvin K or Celsius C or sensor units in volts V millivolts mV or ohms depending on Model number See Paragraph 3 2 3 Baud Selects a Baud Rate of 300 or 1200 for Serial Interface See Par...

Страница 28: ...cal Switches controller between Local LOC and Remote REM operation See Paragraph 3 4 3 SoftCal Improves silicon diode sensor accuracy by setting up a special modification to the Standard Curve 10 See...

Страница 29: ...number All four models permit selection of temperature displays in kelvin K or Celsius C The difference lies in sensor output selection For silicon and GaAlAs diodes Models 330 1X and 3X respectively...

Страница 30: ...ecision Option Calibrations See Table 3 1 To change the curve while pressing the Curve key press the s key to increment the Channel A Curve number or the t key to increment the Channel B Curve number...

Страница 31: ...re For a 2 point SoftCal sense stable temperatures of 77 35 K and 295 K See Paragraph 3 2 7 2 User performed SoftCal has the advantage of nulling both sensor and controller inaccuracies 2 Lake Shore p...

Страница 32: ...oint and generates a new curve from it To verify the new point push the Curve key and use the s or t key to increment the display to the Curve number of the SoftCal curve Verify the Sample display rea...

Страница 33: ...Option breakpoint pairs are loaded in a NOVRAM f or f ield installation Band 2 K 100 K 100 K 305 K 305 K 375 K 11 0 25 K 0 5 K 1 0 K 11A 0 25 K 1 of Temp 12 0 5 K 1 0 K 2 0 K 12A 0 5 K 1 of Temp 13 1...

Страница 34: ...0 Er30 appears if measured heater output does not match the predicted output and the controller turns the heater off Check heater resistance and test for shorts in heater wiring then turn the heater o...

Страница 35: ...er either P PI or PID control Adaptation of an Autotuning algorithm for use at cryogenic temperatures is more complex than for more stable predictable high temperature loads For example over its usefu...

Страница 36: ...w display to OFF then release The controller is now in Manual mode and the user may set gain Proportional see Paragraph 3 3 5 1 reset Integral see Paragraph 3 3 5 2 and rate Derivative see Paragraph 3...

Страница 37: ...As temperature increases system gain normally increases Consequently if sensor sensitivity is relatively constant you can normally increase the controller gain with increasing temperature System gain...

Страница 38: ...Off Low High Heater Range Off Low High Heater Range Off Low High Heater Range Off Low High Heater Range Off Low High Heater Range Off Low High Heater Range Off Low High Heater Range Off Low High P 1...

Страница 39: ...ur terminators are CrLf Carriage Return Line Feed LfCr Line Feed Carriage Return Lf Line Feed End No Terminator EOI line set with last data byte if active To change the IEEE 488 terminators hold the A...

Страница 40: ...odel 330 Power Up PUP configuration to ensure that it powers up to a user defined state after power down Parameters including heater range setpoint gain reset units and curve number store in non volat...

Страница 41: ...ation is selected or not see Paragraph 3 2 4 3 5 4 Thermocouple Compensation From Remote Interface To select or prevent thermocouple compensation over the remote interface use the ACOMP command see Ch...

Страница 42: ...Lake Shore Model 330 Autotuning Temperature Controller User s Manual 3 16 Operation This Page Intentionally Left Blank...

Страница 43: ...f TALKER and LISTENER but cannot be a BUS CONTROLLER The BUS CONTROLLER is the digital computer which tells the MPS which functions to perform Below are Model 330 IEEE 488 interface capabilities SH1 S...

Страница 44: ...l controls if they were previously locked out with the LLO command SPE Serial Poll Enable and SPD Serial Poll Disable Serial polling accesses the Service Request SRQ Status Register This status regist...

Страница 45: ...the setpoint The bit will not revert to zero if the reading falls back outside the chosen limit If this report is read and the control sensor reading is still inside the limit the Model 330 sets the C...

Страница 46: ...Running The Example QuickBasic Program 1 Copy c gpib pc Qbasic qbib obj to the QuickBasic directory QB4 2 Change to the QuickBasic directory and type link q qbib obj bqlb4x lib where x 0 for QB4 0 and...

Страница 47: ...lays the response If no query is sent the instrument responds to the last query received Type EXIT to exit the program NOTE The INPUT instruction accepts no commas as part of an input string If a comm...

Страница 48: ...A EXAMPLE Selecting a primary address of 10 yields the following 10 32 42 Listen address 10 64 74 Talk address F1 Help F6 Reset Value F9 Esc Return to Map Ctl PgUp PgDn Next Prev Board Primary GPIB Ad...

Страница 49: ...ds with the IEEE 488 interface listed in Paragraph 4 3 However without the advantage of the IEEE 488 Architecture there are several limitations No Bus Control Commands apply Only QIDN and QRST Common...

Страница 50: ...riate unit where K kelvin K ENTER COMMAND CDAT Sensor Data Query Controller returns appropriate sensor reading 77 6 ENTER COMMAND TUNE 3 Set Autotuning Status Controller sets Autotuning to PID ENTER C...

Страница 51: ...ION PROGRAM PRINT TIMEOUT 2000 Read timeout may need more BAUD 1200 TERM CHR 13 CHR 10 Terminators are CR LF OPEN COM1 BAUD O 7 1 RS FOR RANDOM AS 1 LEN 256 LOOP1 LINE INPUT ENTER COMMAND or EXIT CMD...

Страница 52: ...annel Query 4 15 SDAT Sample Sensor Data Query 4 15 SUNI Set Sample Units 4 15 SUNI Sample Units Query 4 15 Command Function Page Control Process Commands CLIM Control Limit 4 16 CLIM Control Limit Qu...

Страница 53: ...o enable event flags 0 3 4 and 7 send the command ESE 143 term 143 is the sum of the bit weighting for each bit Bit Bit Weighting Event Name 0 1 OPC 3 8 DDE 4 16 EXE 7 128 PON 143 Q Q Q QESE Query the...

Страница 54: ...he Service Request Enable Register Input SRE Returned SRE bit weighting Format nnn term Remarks The integer returned represents the sum of the bit weighting of the enabled bits in the Service Request...

Страница 55: ...ckout Mode Input MODE 0 MODE 1 or MODE 2 Returned Nothing Remarks Sets the Model 330 mode 0 Local Mode 1 Remote Mode 2 Remote Mode with Local Lockout Press the front panel Local key to set the Model 3...

Страница 56: ...uery Input CCHN Returned A or B Remarks Returns the current control channel setting A channel A B channel B CDAT Control Sensor Data Query Input CDAT Returned 000 00 Remarks Returns control sensor dat...

Страница 57: ...channel setting A channel A B channel B SDAT Sample Sensor Data Query Input SDAT Returned 000 00 Remarks Returns sample sensor data A free field is active here The value returned is 7 characters a si...

Страница 58: ...xample above in the CLIM command returns 001 25 term GAIN Set Gain While In Manual Control Mode Input GAIN XXX Returned Nothing Remarks Enter an integer from 0 to 999 Example GAIN 65 term instructs th...

Страница 59: ...NG Heater Status Query Input RANG Returned 0 1 2 or 3 Remarks Returns current heater status 0 off 1 low 2 medium 3 high RATE Manual Mode Rate Setting Input RATE XXX Returned Nothing Remarks Enter an i...

Страница 60: ...term returns 123 00 term 4 SETP term returns 123 45 term TUNE Sets Autotuning Status Input TUNE X Returned Nothing Remarks Sets Autotuning status 0 Manual 1 P 2 PI 3 PID 4 Zone See Paragraph 3 3 4 for...

Страница 61: ...nsor curve numbers ACUR Curve Number for Channel A Query Input ACUR Returned XX an integer from 00 to 31 Remarks Returns the currently selected sensor curve number for Channel A Table 3 1 lists sensor...

Страница 62: ...CCCC D DDDDD EEE E Y YYYYY ZZZ Z Returned Nothing Remarks If using the IEEE 488 interface enter an entire curve with CURV If using the Serial Interface the 256 character buffer prevents loading the en...

Страница 63: ...YYY ZZZ Z Remarks User must provide curve number 00 thru 31 with query The unit will return header line and all point information for that curve as follows A Curve number from 11 to 31 S For the Model...

Страница 64: ...l 330 recognizes the units field and replaces that data point with the new temperature value FREE Curve Bytes Free Query Input FREE Returned XXXX value from 0000 to 3584 Remarks Returns the number of...

Страница 65: ...instrument and any query response displays EXIT exits the program NOTE The INPUT instruction in this example accepts no commas as part of an input string If a comma appears in an instrument command r...

Страница 66: ...mat CURVE MID CURVE 5 Strip off DRC file header CURVE CURV CURNUM CURVE Add 300 series file header ELSE CURVE CURV CURNUM CURVE Add file header END IF PRINT PRINT COMMANDS SENT TO 320 Screen prints to...

Страница 67: ...0 50 0 1 47551 048 0 1 48412 046 0 1 49606 044 0 1 51300 042 0 1 53706 040 0 1 5525 0 039 0 1 57064 038 0 1 59183 037 0 1 61638 036 0 1 64461 035 0 1 67679 034 0 1 7 1316 033 0 1 75390 032 0 1 79917...

Страница 68: ...Lake Shore Model 330 Autotuning Temperature Controller User s Manual 4 26 Remote Operation This Page Intentionally Left Blank...

Страница 69: ...o power ensure you are plugged into a live outlet and that both ends of the power cord are plugged in Next check the fuse Remove line cord then place a small slotted screwdriver in the slot of the sma...

Страница 70: ...I CHANNEL A CHANNEL B I I V V I PIN Symbol DESCRIPTION 1 2 3 4 5 6 I V I resistor V I diode none Current Voltage Current 1 mA Platinum Voltage Current 10 A Diodes Shield Figure 5 3 Sensor CHANNEL A a...

Страница 71: ...viewed from the Model 330 rear panel 11 12 10 9 8 7 6 5 4 3 2 1 23 24 22 21 20 19 18 17 16 15 14 13 IEEE 488 INTERFACE SH1 AH1 T5 L4 SR1 RL1 PP0 DC1 DT0 C0 E1 PIN SYMBOL DESCRIPTION 1 2 3 4 5 6 7 8 9...

Страница 72: ...21 20 19 18 17 16 15 14 NOT USED 6 5 4 3 2 1 DB25 CONNECTOR RJ11 Receptacle RxD Gnd TxD For Customer supplied computer with DB 25 Serial Interface Connector configured as DCE If the interface is DTE a...

Страница 73: ...master EPROM is U11 DC HEX and the slave is U16 SV HEX The optional Precision Option is provided on a Non Volatile Ram Access Memory NOVRAM IC See Figure 5 9 for locations of these ICs Use the procedu...

Страница 74: ...switches are improperly set Finally Er30 appears if the measured heater output does not match the predicted output The controller turns the heater off Check heater resistance test for shorts in the he...

Страница 75: ...ks refer procedure below to qualified personnel 1 Follow the REMOVE TOP procedure in Paragraph 5 6 2 Select the PT input switch for both inputs A and B See Table 5 1 3 Turn off the heater 4 Allow the...

Страница 76: ...Lake Shore Model 330 Autotuning Temperature Controller User s Manual 5 8 Service Calibration New C 330 U 5 9 Figure 5 9 Typical Model 330 PCB Layout...

Страница 77: ...he actual thermocouple is attached to the input it may be necessary to adjust R28 to correct for any unusual junction effects at the input terminals 5 12 MODEL 330 4X THERMOCOUPLE INTERNAL OFFSET ADJU...

Страница 78: ...Lake Shore Model 330 Autotuning Temperature Controller User s Manual 5 10 Service Calibration This Page Intentionally Left Blank...

Страница 79: ...55 Thermocouple Thermocouple Use the model numbers above to specify input type e g 330 12 for a Model 330 with one Silicon Diode input and one Platinum input The standard 330 heater output is 25 watts...

Страница 80: ...670 K because of their higher sensitivities Only Type K curve is included CURV Command Format Changes To change the thermocouple response signal in millivolts to a voltage equivalent add 45 mV and mul...

Страница 81: ...rollers Mounting brackets and ears to attach two Model 330 Temperature Controllers side by side on a 482 6 mm 19 inch by 88 9 mm 3 5 inch rack mount shelf See Figure 6 5 RM 3H2 H Dual Mounting Shelf f...

Страница 82: ...eters 14 feet C 330 U 6 1 Figure 6 1 Model 2001 RJ 11 Cable Assembly 43 mm 1 69 inches 15 8 mm 0 63 inches 55 mm 2 16 inches 25 1 C 330 U 6 2 wmf Figure 6 2 Model 2002 RJ 11 to DB 25 Adapter 60 3 mm 2...

Страница 83: ...Inch 0 081 2 FHMS Phillips 6 Screw 6 32 x 1 2 inch 0 044 2 PHMS Phillips Additional Parts for Model RM 3H1 H 7 Rack Mount Handle 107 433 2 8 Screw 8 32 x 3 8 inch 0 081 4 FHMS Phillips Item Descriptio...

Страница 84: ...HMS Phillips Item Description P N Qty Remove and discard two screws above front fan slots Replace with two longer screws Item 2 The tabs on the front mounting bracket Item 3 will slide into correspond...

Страница 85: ...004 0 003 0 001 4 000 0 0 00000 0 28930 0 36220 0 41860 0 47220 0 53770 0 59260 0 73440 0 84490 0 92570 0 99110 1 02840 1 07460 1 08480 1 09090 1 09810 1 10800 1 11500 1 12390 1 13650 1 15590 1 18770...

Страница 86: ...l vs Constantan Chromel vs Alumel Copper vs Constantan Number Temp K E VTC mV Temp K K VTC mV Temp K T VTC mV 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 0 0 3...

Страница 87: ...isting inside a furnace for example 1 The values of heat capacity lower Cp and thermal conductivity often higher are such that much shorter thermal time constants Cp are the rule at low temperatures 2...

Страница 88: ...in an audio amplifier but is related to the maximum amount of error signal allowed before the controller is directed to produce full output power The DRC 82C requires a 0 to 8 volt signal from the de...

Страница 89: ...he system and assume that to control at 20 kelvin the heating power required is 0 2 watts Assume also that 50 watts of heater power is available reducible in five steps of one decade each Figure 5 sho...

Страница 90: ...reset control IV PROPORTIONAL GAIN PLUS INTEGRAL RESET TEMPERATURE CONTROL The manual reset adjustment described above varies markedly with the temperature set point and with the often changing heate...

Страница 91: ...tems this time lag can be 10 30 minutes In cryogenic systems it is usually less than a minute even near room temperature Consequently placement of the control sensor with respect to the heater is extr...

Страница 92: ...such resolution have sampling times in the half second range In the world of ovens furnaces and other large industrial processes which operate above room temperature stable control can be maintained b...

Страница 93: ...December 1984 pp 132 136 Some of this material has appeared in Principles of Temperature Control available from Gulton Industries West Division Unlike reference 1 the discussion is not related to cry...

Страница 94: ...7705 1 15558 1 13598 1 12463 1 11896 1 11517 1 11212 1 10945 1 10702 1 10263 1 09864 1 09490 1 09131 1 08781 1 08436 1 08093 1 07748 1 07402 1 07053 1 06700 1 06346 1 05988 1 05629 1 05267 1 04353 1 0...

Страница 95: ...teresting property of the Chebychev fits is evident in the form of the Chebychev polynomial given in Equation 4 No term in Equation 1 will be greater than the absolute value of the coefficient This pr...

Страница 96: ...oom temperature and cryogenic temperatures to guarantee that heat is not being conducted through the leads to the sensor A final thermal anchor at the sample itself is a good practice to assure therma...

Страница 97: ...er Clean both the sensor and mounting surface of any residual flux Next re heat the mounting surface to the melting point of the solder press the device into position and allow the sensor to warm to t...

Страница 98: ...DT 470 CO The CO adapter is a spring loaded clamp to attach the DT 470 SD package to a flat surface It maintains pressure on the SD package as the temperature varies First remove the hold down cap wh...

Страница 99: ...iplying the above sensitivity by the desired temperature resolution in kelvin will give the required voltage resolution in millivolts The static impedance of the DT 470 sensor operating at a 10 microa...

Страница 100: ...reproducibilities to better than 50 mK Figure 1 shows the voltage variation with temperature for a typical silicon diode temperature sensor An error arises in diode thermometry if the excitation curre...

Страница 101: ...0 A Although detailed measurements were taken on only one diode other diodes were randomly selected and spot checked at all three temperatures and frequencies to verify consistency with the measured d...

Страница 102: ...re T the period of integration of the voltmeter or approximately 2 Implied in this derivation is the assumption that is sufficiently small so that effects from diode capacitance on the order of picofa...

Страница 103: ...difference The details of the extended calculation have not been given as the mathematics is somewhat tedious and the slight discrepancies between the small signal model and the extended model do not...

Страница 104: ...housand ohms at a 10 A operating current A capacitor in the range of 10 to 20 F should reduce most noise effects to an acceptable level However because the capacitor increases the time constant in the...

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