User Manual CMC251 1.3 GHz Frequency Counter
Contents
1. Characteristic Measurement Frequency Mode Measurement specifications for frequency mode are applicable for a sine wave applied to the inputs Channel A Range Prescale In Prescale Out 10 MHz to 100 MHz 1 Hzto 10 MHz Channel B Range 80 MHz to 1 3 GHz Accuracy 1 count time base error Channel A Resolution Prescale In Prescale Out 1 Hz to 1 kHz 0 1 Hz to 100 Hz Channel B Resolution 10 Hz to 10 kHz Period Mode Range Prescale In Prescale Out 0 04 us to 1 0 s 0 4 us to 1 0 s Frequency Range Prescale In Prescale Out Sine wave 1 Hz to 25 MHz 1 Hz to 2 5 MHz Accuracy 1 count time base error trigger error Resolution Prescale In Prescale Out 10 ps to 10 ns 100 ps to 100 ns Pulse Mode Range 0 25 us to 500 ms Frequency Range 1 Hz to 2 MHz Accuracy 1 count time base error trigger error 100 ns Resolution 100 ps to 100 ns switchable in four decade steps CMC251 User Manual 21 Appendix A Specifications Table 10 Warranted Characteristics Cont Characteristic Measurement Totalize Mode Range 0 to 99 999 999 counts plus overrange Repetition Rate Sine wave 1Hzto 10 MHz Power Line Voltage Range Selectable ranges at 50 Hz to 60 Hz 90 VAC to 110 VAC 108 VAC to 132 VAC 198 VAC to 242 VAC 216 VAC to 250 VAC Environmental Operating Temperature 10 C to 40 C 72. 2 Front Panel ee Nee ern een 3 Rear Panel 4 2 nee a eee 6 Reference usa esis eee 6 tante nun 9 Making Frequency Measurements 9 Frequencies Below 10 MHZ 9 Frequencies Below 100 MHZ 10 Frequencies Between 80 MHZ and 1 3 GHZ 11 Making Period Measurements 11 Making Pulse Width Measurements 13 Remote Control of Pulse Width Measurements 14 Counting Events 15 Remote Control of TOTAL Mode 16 Checking Instrument Operation 17 Appendix A Specifications 19 Appendix B Maintenance 25 Cleaner ee ee De nan 6 25 Preparing for Shipment 25 Troubleshooting 26 No Display with Power On 26 Appendix C Replaceable Parts 27 Standard Accessories 27 Optional Accessories 27 CMC251 User Manual i Table of Contents List of Tables Table 1 A or B Channel Input 9 Table 2 Selecting Features For Channel A L HZ 10 10 MHZ ann mere Br 10 Table 3 Selecting Features For Channel A 10 MHz to 100 MHz 10 Table 4 Gate Time Versus R
3. lt 25 MHz gt 400 ns lt 2 5 MHz 50mVto5V 3Vto42V 50mVto5V 3Vto42V INPUT LO HI LO HI VOLTAGE button out button in button out button in PRE Button In Button In Button Out Button Out SCALE 3 Press the FUNC button until PERIOD A is indicated with a lighted LED 4 Connect the signal to the CHANNEL A INPUT connector 5 Press the GATE button to select the desired display resolution 12 Refer to Table 7 for the available resolutions Table 7 Resolution For Period Measurements GATE Setting Number of Events averaged PRESCALE In PRESCALE Out xl 10 cycles 1 cycle X10 100 cycles 10 cycles X100 1000 cycles 100 cycles X1000 10000 cycles 1000 cycles CMC251 User Manual Reference Making Pulse Width Measurements A pulse width measurement is the time in seconds from one edge of the signal to the next edge This measurement is accomplished by averaging the signal events for a certain number of internal clock pulses determined by the gate setting Therefore the gate setting determines the resolution or accuracy of the reading The CMC251 Frequency Counter normally measures the positive pulse width but it can measure the negative pulse width using the external input connector on the rear panel This method is discussed in Remote Control of Pulse Width Measurements on page 14 1 Determine the signal voltage level A good practice is to display the signal on an oscilloscope and obtain
4. taxes and any other charges for products returned to any other locations This warranty shall not apply to any defect failure or damage caused by improper use or improper or inadequate maintenance and care Tektronix shall not be obligated to furnish service under this warranty a to repair damage resulting from attempts by personnel other than Tektronix representatives to install repair or service the product b to repair damage resulting from improper use or connection to incompatible equipment or c to service a product that has been modified or integrated with other products when the effect of such modification or integration increases the time or difficulty of servicing the product THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY OTHER WARRANTIES EXPRESSED OR IMPLIED TEKTRONIX AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE TEKTRONIX RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED TO THE CUSTOMER FOR BREACH OF THIS WARRANTY TEKTRONIX AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR HAS ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES SO Table of Contents General Safety Summary iii Getting Started su een 1 Preparing the Frequency Counter for Use
5. 80 MHz and 1 3 GHz Frequencies Below 10 MHz 1 Press the FUNC button until FREQ A is indicated with a lighted LED 2 Refer to Table 2 and set the frequency counter front panel buttons to obtain the best measurement for frequencies below 10 MHz CMC251 User Manual 9 Reference Table 2 Selecting Features For Channel A 1 Hz to 10 MHz 50 mV to 5 V 3 Vto42V INPUT VOLTAGE LO button out HI button in LOW PASS FILTER ON button in ON button in PRESCALE Button Out Button Out 3 Connect the signal to the CHANNEL A INPUT connector 4 Press the GATE button to select the desired display resolution See Tables 4 and 5 for resolution versus gate settings Frequencies Below 100 MHz 1 Press the FUNC button until FREQ A is indicated with a lighted LED 2 Refer to Table 3 and set the frequency counter front panel buttons to obtain the best measurement for frequencies between 10 MHz and 100 MHz Table 3 Selecting Features For Channel A 10 MHz to 100 MHz 50 mV to 5 V 3 Vto42V INPUT VOLTAGE LO button out HI button in LOW PASS FILTER OFF button out OFF button out PRESCALE Button In Button In 3 Connect the signal to the CHANNEL A INPUT input connector 4 Press the GATE button to select the desired display resolution See Tables 4 and 5 for resolution versus gate settings 10 CMC251 User Manual Reference Frequencies Between 80 MHz and 1 3 GHz 1 Press the FUNC button until FREQ
6. avoid electric shock or fire hazard do not operate this product with covers or panels removed Use Proper Fuse To avoid fire hazard use only the fuse type and rating specified for this product CMC251 User Manual iii General Safety Summary Do Not Operate in Wet Damp Conditions To avoid electric shock do not operate this product in wet or damp conditions Do Not Operate in Explosive Atmosphere To avoid injury or fire hazard do not operate this product in an explosive atmosphere Product Damage Precautions Use Proper Voltage Setting Before applying power ensure that the line selector is in the proper position for the power source being used Provide Proper Ventilation To prevent product overheating provide proper ventilation Do Not Operate With Suspected Failures If you suspect there is damage to this product have it inspected by qualified service personnel Safety Terms and Symbols A Terms in This Manual These terms may appear in this manual WARNING Warning statements identify conditions or practices that could result in injury or loss of life CMC251 User Manual General Safety Summary f CAUTION Caution statements identify conditions or practices that could result in damage to this product or other property Terms on the Product These terms may appear on the product DANGER indicates an injury hazard immediately accessible as you read the marking WARNING i
7. in microseconds 5 MHz Indicator Lights when a frequency mode is selected and the PRESCALE button is pressed in indicating that the reading is in megahertz 6 GATE Indicator Lights while the frequency counter is making a measurement The LED extinguishes when updating the display 7 Gate Resolution Indicators These LEDs light to indicate the present gate resolution settings X1 X10 X100 or X1000 8 POWER Switch Powers the instrument on and off 9 GATE Button Determines the display s degree of resolution by setting the gate time the amount of time the counter uses to derive its displayed value The selected resolution is indicated by the lighted LED Each press of the button changes the degree of resolution to the next level 10 FUNC Button Determines the operating mode of the CMC251 Frequency Counter 11 HOLD Button Stops or locks the display when pressed in Toggling the button to its out position allows the measurement to continue When using the TOTAL mode pressing the HOLD button freezes the display but event counting continues 12 RESET Button Sets the display to all zeros new measurements will be displayed after the button is released 4 CMC251 User Manual Getting Started 13 PRESCALE Button Divides the frequency of the signal applied to CHANNEL A INPUT by a factor of ten and sets the measure ment units indicator to either MHz or kHz us When pushed in frequencies up to 100 MHz or period
8. 5 relative humidity Storage Temperature 10 C to 60 C 80 relative humidity 22 CMC251 User Manual Appendix A Specifications Table 11 Certifications and Compliances EC Declaration of Conformity EMC Meets intent of Directive 89 336 EEC for Electromagnetic Compatibility Compliance was demonstrated to the following Specifications as listed in the Official Journal of the European Communities EN 55011 Class A Radiated and Conducted Emissions EN 50081 1 Emissions EN 60555 2 AC Power Line Harmonic Emissions EN 50082 1 Immunity IEC 801 2 Electrostatic Discharge Immunity IEC 801 3 RF Electromagnetic Field Immunity IEC 801 4 Electrical Fast Transient Burst Immunity IEC 801 5 Power Line Surge Immunity EC Declaration of Conformity Low Voltage Compliance was demonstrated to the following specification as listed in the Official J ournal of the European Communities Low Voltage Directive 73 23 EEC amended by 93 68 EEC HD401 S1 Safety Requirements for Electronic Measuring Aparatus Table 12 lists the nonwarranted specifications of the CMC251 Frequency Counter Table 12 Typical Characteristics Characteristic Dimensions H x W xD Measurement 67 mm X 262 mm X 230 mm 2 6 in X 10 3 in X 9 0 in Power Consumption 22 VA 12 W maximum CMC251 User Manual 23 Appendix A Specifications 24 CMC251 User Manual EE Appendix B Maintenance This appendix provides inf
9. B is indicated by a lighted LED 2 After determining that the signal voltage level is 1 V rms or less connect the signal to the CHANNEL B INPUT connector 3 Press the GATE button to select the desired display resolution Refer to Tables 4 and 5 for resolution versus gate settings Table 4 Gate Time Versus Resolution for Channel A GATE Setting Gate Time Resolution PRESCALE Off PRESCALE On X1 0 01 seconds 100 Hz 1 kHz x10 0 1 seconds 10 Hz 100 Hz X100 1 second 1 Hz 10 Hz X1000 10 seconds 0 1 Hz 1 Hz Table 5 Gate Time Versus Resolution for Channel B GATE Setting Gate Time Resolution X1 0 016 seconds 10 kHz X10 0 16 seconds 1 kHz X100 1 6 seconds 100 Hz X1000 16 seconds 10 Hz Making Period Measurements A Period measurement is the time in seconds for a signal to complete one entire cycle This measurement is taken by averaging the signal events for a certain number of internal clock pulses Therefore the gate setting determines the resolution or accuracy of the reading CMC251 User Manual 11 Reference To make a period measurement perform the following steps 1 Estimate the signal source frequency and determine the voltage level A good practice is to display the signal on an oscilloscope and obtain the peak voltage level 2 Refer to Table 6 and set the frequency counter front panel buttons to obtain the best period measurements Table 6 Period Measurements gt 40 ns
10. C251 User Manual 27 Appendix C Replaceable Parts The following power cords are available Table 15 Accessory Power Cords Tektronix Part Plug Configuration Normal Usage Number North America 161 0104 00 115 V Europe 161 0104 06 230 V United Kingdom 161 0104 07 230 V Australia 161 0104 05 Ta 230 V North America 161 0104 08 230 V Switzerland 161 0167 00 230 V 28 CMC251 User Manual
11. ULSE modes CMC251 User Manual Getting Started Figure 3 Rear Panel Signal Connections In Total mode the TTL logic levels start TTL high and stop TTL low the display updates This performs the same function as the HOLD button In Pulse mode the TTL logic levels select either negative TTL low or positive TTL high pulse width measurement CMC251 User Manual 7 Getting Started 8 CMC251 User Manual Reference This section describes typical setups of the CMC251 Frequency Counter for each of its measurement modes Making Frequency Measurements Measuring frquencies with the CMC251 Frequency Counter is simple although there are some items you need to consider before applying the signal to the inputs of the frequency counter 1 Estimate the frequency of the signal source and determine the voltage level This enables you to use the appropriate input channel of the frequency counter A good practice is to display the signal on an oscilloscope and obtain the peak voltage level Refer to Table 1 and pick the appropriate input channel Table 1 A or B Channel Input Estimated Frequency Input Voltage Proper Input Channel 1 Hz to 100 MHz Less than 42 V peak CHANNEL A INPUT 80 MHz to 1 3 GHz Less than 1 Vrms CHANNEL B INPUT 2 Prepare to make a measurement using the steps under one these sections Frequencies Below 10 MHz Frequencies Below 100 MHz or Frequencies Between
12. User Manual Tektronix Z CMC251 1 3 GHz Frequency Counter 070 8527 03 CE Copyright Tektronix Inc 1991 All rights reserved Tektronix products are covered by U S and foreign patents issued and pending Information in this publication supercedes that in all previously published material Specifications and price change privileges reserved Tektronix Inc P O Box 1000 Wilsonville OR 97070 1000 TEKTRONIX and TEK are registered trademarks of Tektronix Inc WARRANTY Tektronix warrants that this product will be free from defects in materials and workmanship for a period of one 1 year from the date of shipment If any such product proves defective during this warranty period Tektronix at its option either will repair the defective product without charge for parts and labor or will provide a replacement in exchange for the defective product In order to obtain service under this warranty Customer must notify Tektronix of the defect before the expiration of the warranty period and make suitable arrangements for the performance of service Customer shall be responsible for packaging and shipping the defective product to the service center designated by Tektronix with shipping charges prepaid Tektronix shall pay for the return of the product to Customer if the shipment is to a location within the country in which the Tektronix service center is located Customer shall be responsible for paying all shipping charges duties
13. al input is no more than 5 V TTL logic level 2 Connect a TTL logic low level 0 volts to the external input connector NOTE Shorting the external input connector to ground accomplishes the same task as applying a TTL logic low 3 The display reading indicates the negative pulse width Changing the TTL logic level to high 5 V enables the frequency counter to measure the positive pulse width Counting Events The CMC251 Frequency Counter can be used to count signal events This feature can be controlled remotely with the use of TTL logic levels applied to the external input connector located on the rear panel Refer to Remote Control of TOTAL Mode on page 16 for a description of its use 1 Determine the signal voltage level A good practice is to display the signal on an oscilloscope and obtain the peak voltage level 2 Setthe Channel AINPUT VOLTAGE switch as necessary determined by the voltage reading obtained in Step 1 3 Press the FUNC button until TOTAL is indicated by a lighted LED 4 Connect the signal to the CHANNEL A INPUT connector The frequency counter will start counting events immediately and continue until the signal is disconnected Pressing the HOLD button freezes the display but the count continues internally The display will update when the HOLD button is toggled out and the count resumes CMC251 User Manual 15 Reference 16 Pressing the RESET button clears the display and
14. e base as a signal source to make a general check of the operating system The display will indicate a frequency of 10 MHz CMC251 User Manual 5 Getting Started A 15 LOW PASS FILTER Button Attenuates signals applied to CHANNEL A INPUT that are above 100 kHz preventing high frequency interference Select this mode to measure signals below 100 kHz 16 INPUT VOLTAGE Button Allows you to select between two levels of input signals for the CHANNEL A INPUT When pushed in the maximum allowable peak to peak input level is from 3 V to 42 V 30 Vrms When in the out position the maximum allowable peak to peak input level is from 50 mV to SV CAUTION To avoid the risk of fire or possible damage to the CMC251 be sure that the equipment generating the signal is properly grounded before you make any connections to the inputs 17 CHANNEL A INPUT Use this connector to measure signals with a repetition rate from 1 Hz to 100 MHz Rear Panel A In addition to the line voltage selectors power input and fuse there is a BNC connector for an external control input located on the rear panel CAUTION To avoid the risk of fire or possible damage to the CMC251 be sure the input equipment is properly grounded before making any connections The external input connector is grounded to the power source ground The external control input see Figure 3 item 1 provides remote control of two instrument functions TOTAL and P
15. e warranty Table 10 Warranted Characteristics Characteristic Measurement Channel A Input Bandwidth 1 Hz to 100 MHz AC coupled Sensitivity Sine wave terminated into 1 MQ 20 mVams 1 Hz to 30 MHz 50 mVams 30 MHz to 100 MHz Impedance 1MQ paralleled by 40 pF Attenuation 3Vto42V Hl 50 mV to 5 V LO Maximum Input Voltage 42 V peak Filter 3 dB at 100 kHz CMC251 User Manual Appendix A Specifications Table 10 Warranted Characteristics Cont Characteristic Measurement Channel B Input Bandwidth 80 MHz to 1 3 GHz AC coupled Sensitivity Sine wave terminated into 50 Q 5 mVrms 80 MHz to 600 MHz 15 mVrus 600 MHz to 900 MHz 35 MVRMS 900 MHz to 1 3 GHz Impedance 50 Q Maximum Input Voltage 1 Vims Internal Time Base Crystal Frequency 10 MHz TCXO Setability 0 1 ppm 1 Hz Temperature Stability lt 0 0001 1 ppm from 0 C to 40 C Line Voltage Stability lt 0 4 ppm with 10 line voltage variation Aging Rate lt 1 ppm yr Display Display Update Time Frequency Mode Period Mode Pulse Mode Totalize Mode Channel A Selected GATE time plus 200 ms interval Channel B Selected GATE time plus 640 ms interval Selected cycles averaging plus 200 ms interval Selected cycles averaging plus 200 ms interval Continuous 20 CMC251 User Manual Appendix A Specifications Table 10 Warranted Characteristics Cont
16. esolution for Channel A 11 Table 5 Gate Time Versus Resolution for Channel B 11 Table 6 Period Measurements 12 Table 7 Resolution For Period Measurements 12 Table 8 Pulse Width Measurements 13 Table 9 Resolution for Pulse Measurements 14 Table 10 Warranted Characteristics 19 Table 11 Certifications and Compliances 23 Table 12 Typical Characteristics 23 Table 13 Standard Accessories 27 Table 14 Optional Accessories 27 Table 15 Accessory Power Cords 28 CMC251 User Manual C General Safety Summary Review the following safety precautions to avoid injury and prevent damage to this product or any products connected to it Injury Precautions Use Proper Power Cord To avoid fire hazard use only the power cord specified for this product Avoid Electric Overload To avoid electric shock or fire hazard do not apply a voltage to a terminal that is outside the range specified for that terminal Ground the Product This product is grounded through the grounding conductor of the power cord To avoid electric shock the grounding conductor must be connected to earth ground Before making connections to the input or output terminals of the product ensure that the product is properly grounded Do Not Operate Without Covers To
17. ndicates an injury hazard not immediately accessible as you read the marking CAUTION indicates a hazard to property including the product Symbols on the Product The following symbols may appear on the product 4 A m DANGER Protective Ground ATTENTION Double High Voltage Earth Terminal Refer to Insulated Manual Certifications and Compliances CSA Certified Power Cords CSA Certification includes the products and power cords appropriate for use in the North America power network All other power cords supplied are approved for the country of use CMC251 User Manual v General Safety Summary vi CMC251 User Manual RE aS Getting Started The Tektronix CMC251 Frequency Counter can make the following frequency related measurements m Frequency measurements up to 1 3 GHz m Period measurements at rates up to 25 MHz m Period averaging of up to 1000 events m Pulse measurements up to 0 25 us m Event counting The 10 MHz internal time base using a highly stabilized crystal oscillator provides a single shot resolution of 100 ns Measurement results are displayed using an eight digit display automatically placing the decimal appropriately The CMC251 Frequency Counter has a locking multiposition handle that folds under the instrument The instrument is delivered with a 115 V power cord an installed fuse for 115 V operation and this manual CMC251 User Manual 1 Getting Started Preparing the Frequency C
18. ormation for the basic maintenance of the CMC251 Frequency Counter Cleaning To clean the frequency counter use a soft cloth dampened in a solution of mild detergent and water Do not spray cleaner directly onto the instrument since it may leak into the cabinet and cause damage Do not use chemicals containing benzine benzene toluene xylene acetone or similar solvents Do not use abrasive cleaners on any portion of the frequency counter Preparing for Shipment If the original packaging is unfit for use or not available use the following packaging guidelines 1 Use a corrugated cardboard shipping carton having inside dimensions at least three inches greater than the instrument dimensions 2 Put the instrument into a plastic bag or wrap to protect it from dampness and loose packing material 3 Place the instrument into the box and firmly stabilize it with packing material 4 Seal the carton with shipping tape CMC251 User Manual 25 Appendix B Maintenance Troubleshooting A 26 Electronic maintenance on the CMC251 Frequency Counter must be performed by a trained technician However an operator can perform some basic and routine maintenance The CMC251 Frequency Counter will give some indications of problems to aid the operator WARNING To prevent electrical shock unplug the power cord and disconnect the signal input cable from any signal source before checking or replacing the fuse No Di
19. ounter for Use Check the following items prior to operating the frequency counter for the first time see Figure 1 for locations of items 1 through 3 1 3 un Ha din Figure 1 Line Voltage Selectors Power Input and Fuse Locations CAUTION To prevent damage to the instrument set the line voltage selectors to the proper voltage setting and install the correct line voltage fuse before operating the equipment 1 Set the line voltage selectors to the input line voltage These selectors connect internal wiring for various line voltages This product is intended to operate from a power source that does not supply more than 250 Vrms between the supply conductors or between either supply conductor and ground For line voltage ranges refer to Appendix A Specifications on page 19 WARNING To prevent electrical shock unplug the power cord and disconnect the signal input cable from any signal source before checking or replacing the fuse 2 Check that the correct line fuse is installed The line fuse provides protection if the equipment malfunctions or an overload occurs Refer to Appendix C Replaceable Parts on page 27 for fuse part numbers 2 CMC251 User Manual Getting Started WARNING To prevent electrical shock connect the power cord to a VAN properly grounded power source The outside ground of this connector is connected through the equipment to the powe
20. r source ground Do not remove the ground lug from the power cord for any reason 3 Connect the input power cord Use only the power cords specified for this equipment Refer to Appendix C Replaceable Parts on page 27 for power cord part numbers Front Panel Figure 2 shows the front panel controls connectors and indicators with brief descriptions of the items following the figure I LA oo 17 16 15 14 1312 11 10 9 8 7 Figure 2 Front Panel Controls Connectors and Indicators CAUTION To avoid the risk of fire or possible damage to the CMC251 be sure that the equipment generating the signal is properly grounded before you make any connections to the inputs 1 CHANNEL B INPUT Button Use this input connector to measure signals with a repetition rate from 80 MHz to 1 3 GHz CMC251 User Manual 3 Getting Started 2 OVERRANGE Indicator Lights when frequencies above the specified limits are applied to either channel 3 Display The display area provides measurement information on the digital display Single LEDs indicate the units and conditions of the display 4 kHz us Indicator Lights when a frequency mode is selected and the PRESCALE button is in its out position indicating that the reading is in kilohertz When the period or pulse mode is selected the LED lights to indicate the reading is
21. resets the count back to zero The count resumes when the RESET button is released Remote Control of TOTAL Mode Refer to Figure 5 for the setup diagram for remotely controlling the TOTAL mode 1 Perform Steps 1 through 4 of Counting Events on page 15 2 Connect a signal source that can apply TTL logic levels of low and high 0 V and 5 V to the external input connector CAUTION To avoid damage to the CMC251 Frequency Counter ensure that the maximum voltage into the rear panel input is no more than 5 V TTL logic level To External Input connector on rear panel Signal source TTL Signal source C FN CHANNEL INPUT Figure 5 Setup for Remote Control of TOTAL modes CMC251 User Manual Reference 3 Control the TOTAL mode by applying a TTL logic signal to the external input connector as folows m Apply a low level 0 volts to stop the count same as the HOLD button m Apply a TTL logic high level 5 V to resume the count same as releasing the HOLD button Checking Instrument Operation At any time you can verify the accuracy of the CMC251 Frequency Counter by using the CHECK function Press the FUNC button until CHECK is indicated by the lighted LED The readout will display 10 000 MHz CMC251 User Manual 17 Reference 18 CMC251 User Manual i Appendix A Specifications Table 10 and 11 list the characteristics of theCMC251 Frequency Counter that are guaranteed by th
22. s up to 0 04 us can be measured In the out position frequencies up to 10 MHz or periods up to 0 4 us can be measured 14 Mode Indicators These LEDs light to indicate the present mode settings One of the following modes is indicated m FREQ A The Frequency A mode measures the repetition rate of the signal applied to the CHANNEL A INPUT In this mode measurements from 1 Hz to 100 MHz can be made m FREQ B The Frequency B mode measures the repetition rate of the signal applied to the CHANNEL B INPUT In this mode measurements from 80 MHz to 1 3 GHz can be made m PERIOD A The Period A mode measures the time it takes for one cycle of the signal applied to CHANNEL A INPUT to be completed m PULSE A The Pulse A mode measures the width of the positive pulses of the signal applied to CHANNEL A INPUT The Pulse mode can also measure the negative pulse of the input signal when using the external control input connector located on the rear panel See Making Pulse Width Measure ments on page 13 for a description of its use TOTAL The Totalize mode counts signal events applied to CHANNEL A INPUT incrementing one count for each event The display is updated continuously unless the HOLD button is pressed The count resumes when the HOLD button is released The Totalize mode can also be controlled remotely with the use of the external control input connector located on the rear panel m CHECK The Check mode uses the internal tim
23. splay with Power On If the digital display is not lighted but the POWER button is pushed in and the CMC251 Frequency Counter power cord is plugged into an outlet do the following steps 1 Check the line fuse If the fuse is open replace it 2 If the line fuse is good check the power outlet for proper voltage If the outlet voltage is incorrect call service personnel WARNING To prevent electric shock disconnect the power cord from the power source and the CMC251 Frequency Counter before checking continuity 3 If outlet voltage is correct check power cord continuity If the power cord fails the continuity check replace the power cord CMC251 User Manual iE SSS Appendix C Replaceable Parts Replaceable parts may be ordered directly from your authorized Tektronix dealer Standard Accessories The following items are shipped with the CMC251 Frequency Counter Table 13 Standard Accessories Accessory Tektronix Part Number Fuse 3AG 0 3 A 250 V SB 159 0029 00 90 132 V operation User Manual 070 8527 XX 115 V Power Cord Refer to Table 15 Optional Accessories The following items are available as optional accessories Table 14 Optional Accessories Accessory Tektronix Part Number Fuse 3AG 0125 A 250 V SB 159 0313 00 198 250 V operation 230 V Power Cords Refer to Table 15 36 inch 50 Q BNC cable 012 1341 XX 66 inch 50 Q coaxial cable signal 103 0275 XX adapter CM
24. the peak voltage level 2 Refer to Table 8 and set the frequency counter front panel buttons to obtain the best pulse measurements Table 8 Pulse Width Measurements 50 mV to 5V 3Vto42V INPUT VOLTAGE LO button out HI button in LOW PASS FILTER OFF button out OFF button out PRESCALE No Effect No Effect 3 Press the FUNC button until PULSE A is indicated by a lighted LED 4 Connect the signal to the CHANNEL A INPUT connector 5 Press the GATE button to select the desired display resolution See Table 9 for the available resolutions CMC251 User Manual 13 Reference Table 9 Resolution for Pulse Measurements GATE Setting Number of Events Averaged xl 1 cycle X10 10 cycles X100 100 cycles X1000 1000 cycles Remote Control of Pulse Width Measurements The frequency counter normally measures the positive pulse width of the applied signal The negative pulse width can be measured with the use of the external input connector on the rear panel Refer to Figure 4 for a setup diagram To External Input connector on rear panel Signal source TTL Signal source G N CHANNELA INPUT Figure 4 Setup for Remote Control of Pulse Width Measurements 1 Perform steps 1 through 5 of Making Pulse Width Measurements on page 13 14 CMC251 User Manual Reference CAUTION To avoid damage to the CMC251 Frequency Counter ensure that the maximum voltage into the rear panel extern
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