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1. Frequency measurement accuracy is determined by the following two conditions 1 HAcount 2 Time base accuracy The count error is inherent to digital meters and is produced by the phase relationship between the gate signal and the input signal shown in Fig 7 The counted result of 1 count increased or decreased depends on the phase difference Gate Signal pa l l l 2 counts l l l Shaped output l l l l l 3 counts l Shaped output Fig 7 count error 152. EA a e 6 CIRCUIT DESCRIPTION 6 1 Theory of Operation Measurement Accuracy 6 2 Frequency Measurement Accuracy In order to get the most benefit from the frequency counter it s useful to comprehend the circuit thoroughly We have attempted every possible to utilize the latest developments in large scale integration to provide the greatest performance for the money and at the same time to reduce the complexity of circuit and increase reliability Ignoring the prescaler for the moment let us assume the input signal arrives at the 1OMHz to 100MHz input labeled CHA in main board This signal is first amplified by the Q201 Q202 pair The three amplifier stages identified as U202 in the schematic are ECL logic stages biased in its linear region each stage having a gain before feedback of about 5 A positive feedback at the output of the third amplifier when reflected through the gain of the proceeding three amplifier states including the Q201 Q202 pair results in about a 5mV hysteresis in the input triggering levels to aid in noise rejection Q203 and Q204 translate the ECL levels to TTL levels The signal is presented directly to the counter IC U301 The IC U301 provides all the functions of the counter and display result through LED U201 regulates the input 9 volts signal from the line voltage transformer and rectifier circuit When the power switch is set to on position approximately 5 0 volts is applied to the circuit 14
3. Test Equipment Depot 99 Washington Street Melrose MA 02176 6024 www testequipmentdepot com 800 517 8431 781 665 0780 FAX FREQUENCY COUNTER FREQUENCY COUNTER USER MANUAL USER MANUAL L m CONTENTS PAGE 1 PRODUCT INTRODUCTION ccccccccscssscsssssrsesersesees 1 1 1 Description ccceccccceccccceccccccccccnccecceseeecees 1 12 Featuren e oes vas see sincesedsce deesses sehen ses SERS 1 2 TECHNICAL SPECIFICATION ccccecsecceseeeees 2 3 PRECAUTIONS BEFORE OPERATION 0se0 3 3 1 Unpacking the Instrument ccccecceccececeecees 3 3 2 Checking the Line Voltage ssescssssscccecseeees 3 3 3 Equipment Installation and Operation se0 4 3 4 General Preparation cccccccececcccccccecceccecseses 4 4 PANEL INTRODUCTION cccccececcesceccsceees 5 5 APPLICATIONS ssisiengeasivescssesereste cpu ste Sko sae r 7 5 L SenSitivity ccccecceccecceccencceccecccececescnsseseeeseeees 7 5 2 Input Sensitivity Characteristic ccccececcceceeese 10 5 3 Maximum Input Voltage ccecceceeeeccceceeceeees 11 54 Typical Applications cccccececcccceccecceceesees 11 6 CIRCUIT DESCRIPTION cccccesceceeseec cee cveee sees 13 6 1 Theory of O peration cecceccecceccecceccscscsceees 13 6 2 Frequency Measurement ACCUIaCyY ceceecceceeee 14 Ts MAINTENANCE cniceiseisccsessccsiccesedacseccecssedsnvsas
4. e waveform it will not occur erroneous counting with any magnit ude input lower than the input destroyed voltage 5 2 Input Sensitivity Characteristic The input sensitivity of this instrument is shown as Fig 5 SENSITIVITY mVrms 100Hz 30MHz 60MHz 120MHz 150MHz Fig 5 Input Sensitivity Characteristic 11 Test Equipment Depot 99 Washington Street Melrose MA 02176 6024 FREQUENCY COUNTER USER MANUAL E 5 3 Maximum input voltage The maximum input voltage Vs frequency characteristics is shown as Fig INPUT VOLTAGE Vrms 150 NOTE These Values must not be exceeded when the signal contains a DC Component DC Voltage peak AC Voltage 1KHz 50 100KHz 1MHz 100 150 Fig 6 Maximum Input Voltage Frequency 5 4 Typical Applications Several examples for typical applications are described below 1 The output frequency of a transmitter or transceiver can be measured if the output power is about 1W by merely connecting a one turn clip cord to several tens of centimeters from antenna The length of the distance is determined by the magnitude of the output 12 www testequipmentdepot com 800 517 8431 FREQUENCY COUNTER USER MANUAL T 2 Measurement can also be easily performed when calibrating the oscillation frequency of a grid dip meter by merely connecting the one turn clip cord 3 Measurement of tracking the frequency through the oscillator stage multiplier stage and output stage can be perf
5. ormed by making a small 2 3 turn coil and coupling it to each turned circuit the oscillations may be produced by the input capacitance and its resonant frequency with too many turns of coil Note As the product has a high sensitivity induction may cause erroneous counting if you touch the red end ungrounded side of the clip cord Therefore hold the black clip or coaxial cable when performing measurements according to above method Measurement by connecting the accessory cable directly to the test circuit is described below 4 Measurement can generally be jerformed by merely connecting the black side of the clip cord to ground GND and the red side to the test point 5 When the capacitance of the cable will have an affection on the test circuit When measuring turned circuits or high output impedance circuit perform measurement by inserting a high resistance in series with the red side of the clip cord Always be sure to ground the cord when perform the measurement of 4 and 5 above If possible ground the cable to the ground point of the test circuit This procedure will reduce the affection of noise A wide variety of measurement can be conceived in addition to 1 5 fully utilizing the special features of the counter 13 781 665 0780 FAX Test Equipment Depot 99 Washington Street Melrose MA 02176 6024 www testequipmentdepot com 800 517 8431 781 665 0780 FAX FREQUENCY COUNTER FREQUENCY COUNTER USER MANUAL USER MANUAL T
6. quipment Depot 99 Washington Street Melrose MA 02176 6024 FREQUENCY COUNTER USER MANUAL a 5 APPLICATION 5 1 Sensitivity The role of the SENSITIVITY or attenuator switch in a common measuring instrument is to protect the input circuit and prevent the meter from going off scale For a counter SENSITIVITY is still one of the large roles Generally hysteresis occurs in the waveshaping circuit of the counter In order for the instrument to put up resistance to noise the circuit will not work even when the noise is lower than the hysteresis applied The waveshaping circuit is a Schmitt circuit and the operation of this circuit is described below VH V V VH Hysteresis voltage Input Voltage V H v y OH Output Voltage v OL Fig 2 Operation of the Schmitt circuit www testequipmentdepot com 800 517 8431 781 665 0780 FAX FREQUENCY COUNTER USER MANUAL As refer to Fig 2 when input voltage is at V the output voltage is high Vou while input voltage is at V the output voltage is low VoL The difference between these two voltage Vy V V is called the hysteresis voltage But if both V and V don t react each other no output will be obtained and the Schmitt circuit will not work out with the states of 1 2 and 3 of Fig 3 shown as below 1 2 Fig 3 States under which the schmitt circuit doesn t work From above description it can be easily understood whether or not the Schmi
7. seneeses 18 7 1 Standard Method for Calibration ccseseeeeee 18 TL CIOAMING eeren erea o eSa cesedstecedeceecd coseeaecs 18 Test Equipment Depot 99 Washington Street Melrose MA 02176 6024 FREQUENCY COUNTER USER MANUAL a 4 PANEL INTRODUCTION 1 Counter Input BNC type connector 2 ATT 1 1 1 10 Attenuation button of input sensitivity 1 1 Directly connect input signal to input amplifiers 1 10 Attenuate input signal by a factor of 10 3 LPF ON OFF Set to ON position insert a 100kHz Low Pass Filter intc input for low frequency measurement 4 FREQ PRID Frequency or period measurement by setting the button 5 Gate Time Selector Press the gate time button to 10 sec 1 sec or 0 1 sec for measurement 6 Power ON OFF Power on or off by using the button 7 Gate Time LED The gate time of 10 sec 1 sec or 0 1 sec will be displayed in the LED by setting the Gate button 8 Over LED Overflow indicator shows that one or more of the most significant digits are not displayed 9 Displayed LED Display 8 digits of frequency data 10 Exponent and units LED indicator shows S and Hz of the unit and indicate LED the value of the measurement exponent as shown below k 1000 M 1 000 000 G 1 000 000 000 m 1 1000 p 1 1 000 000 n 1 1 000 000 000 www testequipmentdepot com FREQUENCY COUNTER 800 517 8431 USER MANUAL 781 665 0780 FAX Front Panel Fig 1 Front panel Test E
8. tt circuit works is attributed to the SENSITIVITY Attenuator to determine the magnitude of the input voltage An example of preventing erroneous counting by correctly selecting the SENSITIVITY shown as Fig 4 below a Correctly counting a distortion signal by selecting suitable SENSITIVITY However when the input voltage is too high a frequency doubles the unknown frequency will be indicated b Erroneous counting occurs when high frequency noise is superimposed on the unknown signal and the input voltage of the Schmitt circuit is too high However a correct counting can be obtained by selecting suitable SENSITIVITY Test Equipment Depot 99 Washington Street Melrose MA 02176 6024 FREQUENCY COUNTER USER MANUAL E a When unknown signal is distorted b When high frequency noise superimposed on unknown signal Fig 4 10 www testequipmentdepot com 800 517 8431 781 665 0780 FAX FREQUENCY COUNTER USER MANUAL The erroneous counting can be prevented by satisfying two conditions below a To make peak to peak value of the noise voltage smaller than Vy b When peak to peak value of unknown signal is larger than Vy perform measurements by first setting SENSITIVITY to 1 10 then set it to 1 1 range to protect the input circuit and avoid erroneous counting One good method is to conduct measurements at the smallest possible input within the counter display value dispersion range When the signal is a pur
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