FLUKE pm6685r 电路图.pdf

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1、Programmable Frequency Counter PM6685 rather, it is concerned primarily with those parts of the instrument which are essential for determining the function of the instrument. It is not necessary to remove the cover of the instrument to perform this procedure. If the test is started less than 20 minu

2、tes after turning on the instru- ment, results may be out of specification, due to insufficient warm-up time. Recommended Test Equipment *) Two of the cables must have 10 ns difference in delay, for ex- ample: 5 ns and 15 ns. Preparations Power up your instruments at least 20 minutes be- fore beginn

3、ing the tests to let them reach normal operating temperature. Failure to do so may result in certain test steps not meeting equipment specifi- cations. Front Panel Controls Power-On Test At power-on the counter performs an automatic self-test of the fol- lowing: Microprocessor RAM ROM Measuring circ

4、uits Display If a GPIB interface is installed, the GPIB address is displayed. If there are any test failures, an error message is shown. Turn on the counter and check that all segments light up on the display and that no error message appears. Internal Self-Tests The different built-in test routines

5、 invoked by the power-on test can also be activated from the front panel as follows: Enter the Auxiliary Menu by pressing AUX MENU. Select the test submenu by pressing DATA ENTRY up or down. Enter the test menu by pressing the ENTER key. Selections for internalself-tests are: 1TEST ALL (Test 2 to 5

6、in sequence) 2TEST RO (ROM) 3TEST RA (RAM) 4TEST LOGIC (Measuring Logic) 5TEST DISP (Display Test) Use DATA ENTRY up/down to select TEST ALL, then press ENTER. If any fault is detected, an error message appears on the dis- play and the program halts. If no faults are detected, the program returns to

7、 measuring mode. 2-2Performance Check, General Information Type of instru- ment Required Specifications Suggested Equipment LF SynthesizerSquare; Sine up to 10 MHz Power Splitter50 ?PM9584/02 T-piece Termination50 ?PM9585 Reference oscilla- tor 10 MHz 0.1 Hz for standard oscillator Fluke counter wit

8、h calibrated option PM9691 10 MHz 0.01 Hz for PM9691 press menu again. Short Form Specification Test Sensitivity and Frequency Range Press the PRESETkey to set the counter in the default setting. Then confirm by pressing ENTER. Turn off AUTO. Select IMP A = 50 ? and maximum sensitivity. Connect a si

9、gnal from a HF generator to a BNC power splitter. Connect the power splitter to your counter and an oscilloscope. Set input impedance to 50 ? on the oscilloscope. Adjust the amplitude according to the following table. Read the level on the oscilloscope. The counter should display the correct frequen

10、cy. Reference Oscillators X-tal oscillators are affected by a number of external conditions, suchasambienttemperatureandsupplyvoltage,buttheyarealsoaf- fected by aging. Therefore, it is hard to give limits for the allowed frequency deviation. You must decide the limits depending on your application,

11、 and recalibrate the oscillator accordingly. See the Pre- ventive Maintenance in the Repair chapter, Chapter 5. To check the accuracy of the oscillator you must have a calibrated reference signal that is at least five times as stable as the oscillator that you are testing, see the following table. P

12、ress the PRESETkey, then press the ENTER key to set your counter in the Default setting. Performance Check, Short Form Specification Test2-3 Key(s)DisplayNotePass /Fail STAND-BYDisplay OffRed LED beside the key On ONBacklight on PRESET ENTER DEFAULT? NO SIGNAL Default setting EXT REFEXT REF Input A

13、FILTERFILTER 50? 50 ? (2 times) SENS ? (2 times) Bar graph: ? SENS ? (2 times) Bar graph: ? AUTOAUTO TRIG Other PRESET ENTER DEFAULT? NO SIGNAL Default setting MEAS TIME2003s DATA ENTRY ?5003s DATA ENTRY ?2003s ENTERNO SIGNAL DISPLAY HOLDHOLD DISPLAY HOLD SINGLESINGLE FUNCTION ?DUTY F A FUNCTION ?TO

14、T A MAN FUNCTION ?DUTY F A FUNCTION ?FREQ A AUX MENURECALL MEAS RESTARTNO SIGNAL PRESET ENTER DEFAULT? NO SIGNAL Default setting CHECK10.000000006Hz*Start counting NULLNULL NULL10.000000006Hz* BLANK DIGITS (3 times) 10.00000? ? ?6Hz* MENUDisplays all avail- able functions, pro- cesses and input cont

15、rols. Selected items are blinking. Table 2-2Keyboard Test. FrequencyLevelPass/Fail MHzmVPPmVRMSdBmInput A 1301027 25301027 50301027 150602021 200903017 25015050-13 30015050-13 Table 2-3Sensitivity of input A at various frequencies. OscillatorMax. tempera- ture dependence Max. aging per month Max. ag

16、ing per year Standard100 Hz5 Hz50 Hz PM96910.05 Hz0.1 Hz0.75 Hz PM96920.025 Hz0.03 Hz0.2 Rubidium0.003 Hz0.0005 Hz0.002 Hz Table 2-4Deviation (for PM9691 and PM9692 after a warm-up period of 48 hours). Connect the reference to input A. Check the readout against the accuracy requirements of your appl

17、ication. ?Acceptance Test As an acceptance test, the following table gives a worst case figure after a 30 minute warm up time. All deviations that can occur in a year are added together. ?Acceptance Test, PM6685R To fully test the accuracy of the PM6685R, a reference signal of ex- tremely high stabi

18、lity is needed. Examples of such references are Cesium Atomic references, or transmitted signals from a nationally or internationally traceable source, like the GPS satellites. Recommended Test Equipment TypeStabilityModel 10 MHz refer- ence ? 1x10-10910R with satellite contact dur- ing the last 72

19、hours. Test Procedure Connect the counter to the line power. Check that the UNLOCK indicator turns on, and then turns off again within 6 minutes after connecting line power. Connect the 10 MHz reference signal to input A of the counter. Select FREQUENCY A measurement. Select 2 s measuring time. Chec

20、k that the displayed frequency is 10.00000000 MHz 0.05 Hz ? 10 minutes after connection to line power. Rear Input/Output INT REF Output Connect an oscilloscope to the 10 MHz output on the rear of the counter. Use coaxial cable and 50 ? termination. The output voltage is sinusoidal and should be abov

21、e 2.8 VPP. EXT REF Input Press the PRESET key, then press the ENTER key to set your counter in the Default setting. Apply 10 MHz sine to input A equipped with a T-piece and to Ext Ref input at the rear, terminated with 50 ?. Amplitude on 10 MHz signal; 200 mVRMS, (560 mVPP) Press the Ext Ref key. Th

22、e display should show 10.000000006Hz 5 LSD. EXT ARM INPUT Press the PRESETkey, then press the ENTER key to set your counter in the Default setting. Select 50 ?input impedance. Apply 10 MHz 500 mVRMS, (1.4 VPP) sine to input A The counter measures and displays 10 MHz. Press the AUX MENU key. Press th

23、e DATA ENTRY UP/DOWN keys until the display shows Ar. Start, confirm by pressing the ENTER key. Press DATA ENTRY UP/DOWN keys until the display shows POS, confirm by pressing the ENTER key. Press the ENTER key once more. The counter does not measure. Connect a pulse generator to Ext Arm input. Setti

24、ngs for pulse generator: single shot pulse, amplitude TTL = 0 - 2 VPP, and duration = 10 ns. Apply one single pulse to Ext Arm input. The counter measures once and shows 10 MHz on the display. Measuring Functions Preparation for Check of Measuring Function is as follows: Connect a 10 MHz sine wave s

25、ignal with 2.0 VPPamplitude via a T-piece to Input A. Connect a cable from the T-piece to Input E (Ext Arm) at the rear. Select the measuring function as in the Selected Function col- umn and check that the counter performs the correct measure- ment by displaying the result as shown under the “Displ

26、ay” column in the following table. 1) Value depends on the symmetry of the signal. 2) Exact value depends on the input signal. 2-4Performance Check, Rear Input/Output OscillatorFrequency readoutSuitable refer- ence Pass /Fail Standard10.00000000 MHz 120 Hz PM9691 PM969110.00000000 MHz 1 HzPM6685R PM

27、6681R PM969210.00000000 MHz 0.25 Hz Table 2-5Acceptance test for oscillators. Selected FunctionDisplayPass/ Fail PRESET ENTER DEFAULT? 10 MHz 2) IMP A 50 ?10 MHz 2) Non AUTO10 MHz 2) PER A100 ns 2) RATIO A/E1.0000000 PWIDTH A50 ns 1) TOT A MAN DISPLAY HOLDStart counting DISPLAY HOLDStop counting DUT

28、Y FACT0.500000 1) AUTO0.500000 1) Table 2-6Measuring functions check. Options Prescaler This extra HF input (PM9624) is easily recognized by its front panel connector (Input C, type N). Connect the output of the signal generator to the HF input of the counter. Connect the 10 MHz REFERENCE OUT of the

29、 generator to the REFERENCE IN at the rear panel of the counter. Setting for the counter after Preset. Function = FREQ C. EXT REF. Generate a sine wave in accordance with the following table. Verify that the counter counts correctly. (The last digit will be unstable). Performance Check, Options2-5 F

30、requencyAmplitudePass/Fail MHzmVRMSdBm 100-3002021 -25001027 -27002021 -30001007 Table 2-7Sensitivity of the PM9624 HF input. EXT REF Fig 2-2Connect the output of the signal generator to the HF input of the counter. Required Test EquipmentSuggested Specification HF signal generator3.3 GHz Table 2-8T

31、est equipment for 3.0 GHz HF input. This page is intentionally left blank. 2-6Performance Check, Options Chapter 3 Disassembly The terms in the following figure are used in all descriptions in this manual. The PM6685 is available with a number of options and accessories. The labels on the rear panel

32、 of the counter identify the options and accessories included. If there are no labels, the counter contains an uncompensated crystal oscillator and no options. The following la- bels exist: PM9624 3.0 GHz HF input PM9691 High-Stability Oven Oscillator PM9692 Ultra-High-Stability Oven Oscillator PM96

33、26B GPIB Interface The location of these optional parts is illustrated in Fig.3-2. Removing the Cover WARNING: Do not perform any internal service or ad- justment of this instrument unless you are qualified to do so. WARNING: When you remove the cover you will ex- pose high voltage parts and accessi

34、ble terminals which can cause death. WARNING: Although the power switch is in the off position, line voltage is present on the printed cir- cuit board. Use extreme caution. WARNING: Capacitors inside the instrument can hold their charge even if the instrument has been sepa- rated from all voltage so

35、urces. Make sure the power cord is disconnected from the counter. Turn the counter upside down. Loosen the two screws (A) at the bottom and the two screws (B) in the rear feet. Grip the front panel and gently push at the rear. Pull the counter out of the cover. Reinstalling the Cover Gently push the

36、 counter back into the cover. Turn it upside down. Install the two screws (A) at the bottom. Install the two rear feet with the screws (B) to the rear panel. PM9624 (HF Input) Disconnect the power cable. Remove the cover from the counter. Disconnect the cable from the mini-coax connector (A) on the

37、HF input. Press the clips (B) apart and lift the HF input pca straight up and out. 3-2Disassembly, Removing the Cover Top Left Right FrontBottom Rear Fig. 3-1Designations used in this manual. G 1 Main board Front panel Power Module GPIB interface Optional oscillator HF input Fig. 3-2Location of the

38、boards in the counter. A B A B Fig. 3-3Remove the screws and push the counter out of the cover. When installing the HF input, make sure that the connector pins fit exactly in the holes in the connector housing (C). PM9626 (GPIB Interface) Disconnect the power cable. Remove the cover from the counter

39、. Loosen the two screws (A) holding the GPIB interface to the rear panel. Disconnect the interface cable from P103. Move the GPIB interface pca toward the front of the counter and lift the pca supports out from the “keyholes” (B) on the main PCA. PM9691 or PM9692 (Oven Oscillator) Disconnect the pow

40、er cable. Remove the cover of the counter. Remove the two screws (A) holding the oscillator to the main pca from underneath. Press the clip (B) gently to the front of the counter and lift the oscillator straight up. Make sure that jumpers J14 and J15 are set in the correct posi- tion. When fitting t

41、he oscillator, make sure that the connector pins fit exactly in the holes in the connector housing. Disassembly, PM9626 (GPIB Interface)3-3 B A B A Fig. 3-4Loosen the two screws in the rear panel and dis- engage the board from the keyholes. A Fig. 3-5One of the two screws holding the oven oscillator

42、 in place. A B B C Fig. 3-6Removing the HF Input. This page is intentionally left blank. 3-4Disassembly, PM9691 or PM9692 (Oven Oscillator) Chapter 4 Circuit Descriptions Block Diagram Description General The PM6685 Frequency Counter consists of three main units: Front unit Main board unit Rear pane

43、l unit The following options can be added: GPIB interface including analog output (PM9626B) Prescalers 1.3 GHz (PM9621), 3.0 GHz (PM9624) Oven-controlled crystal oscillators (PM9691 or PM9692) Rack mount adapter (PM9622/02) Battery option (PM9623) The chassis of the counter consists of a front piece

44、 molded in alumi- num, an aluminum rear panel, and two profiled aluminum rods that hold the front and rear panels together. This unit can be slid into the aluminum cover of the instrument. The front unit contains all functions needed for the user communica- tion. It is connected to the main board un

45、it with a flat cable, and the molded front unit is fixed to the two profiled aluminum rods with screws. The main board unit consists of a PCB mounted on two profiled alu- minumrods.Mostfunctions,suchasthefollowing,areplacedonthe main board: Input amplifiers with trigger level circuits Power supply M

46、easurement logic Microcomputer circuitry Some outputs, such as the trigger levels and probe compensation view outputs are directly mounted on the main board. The rear panel unit is of aluminum with a number of mounted con- nectors. Most of the connectors are soldered directly to the main board.There

47、arpanelisfixedtothetwoprofiledaluminumrodswith screws. 4-2Block Diagram Description Block Diagram Description4-3 Local preset Optional oscillator External arming External reference HF input InputAmplifier Reset circuit Power supply 90-265 V Micro- computer Counter ASIC 10 MHz out Gate LED Display An

48、alog output GPIB option Keyboard +7V +5V -5.2V AC I C 2 PWM E C D A G RESET U11 HSI.0 X2 EXTC B2 EXTREF A A2 U29 GET Trigger DACs INTREF 2 +12V Option 80 Fig. 4-1PM6685 block diagram. Hardware Functional Description Front Unit LCD Drivers An LCD and two LEDs are used as indicators. The LCD is used t

49、o show both the measurement result and the state indicators of the in- strument setting. The LEDs show standby and gating. The LCD has 158 segments that are multiplexed with a ratio of 2:1. Two parallel and synchronized LCD drivers (U201 and U202) are used. They are connected with a serial I2C bus to the microcomputer on the main board. The clock frequency of the drivers is approxi- mately 140 kHz, set by R201. The VLCD pin is connected to GND on the main board. The LCD is provided with a backlight, an LED array integrated into one component. Its current consumption