Extech Instruments 381235 Manuale utente

User's Guide

Frequency Counter

Model 381235

Introduction

Congratulations on your purchase of Extech’s Frequency Counter. This meter will measure

frequency to 2.5GHz using test leads or the optional RF antenna. This professional meter,

with proper care, will provide years of safe reliable service.

381235 Ver. 1.5 3/01

Specifications

General Specifications

Display 0.5” (13mm) 8-digit LCD

Functions Frequency, Data Hold, Relative, Max/Min/Avg & Period

Input connectors BNC female

Meter housing Durable ABS plastic

Operating conditions 32 to 122oF (0 to 50oC); < 90% RH

Power supply 4 x 1.5V AA cells

105mA DC approx. 2500MHz/500MHz rangesPower consumption 45mA DC approx. for 10MHz & Period ranges

AC adapter (option) 9VDC, 300 to 500mA (center socket pin positive)

Dimensions; weight 6.8 x 3.1 x 1.4” (173 x 80 x 35mm); 0.75 lbs (340g)

Electrical Specifications

Ch. A: 2500MHzFrequency range Ch. B: 500MHz

Period range Ch. C: 10MHz

Resolution, sample rate and

sensitivity Refer to Sections 2.3 and 2.4 below

Accuracy ± (4 ppm + 1 digit) @ 23oC ±5oC

Time base 4.194 MHz quartz crystal

Temp. coefficient 0.1 ppm per oC typical

5V peak to peak max. for 2500/500MHz rangeInput overload 250V peak to peak max. for 10MHz & Period range

Resolution and sampling rate specifications

Range Gate time selection Resolution (Hz) Sampling time (sec)

FAST 1000 0.5

SLOW 100 2.75

SLOW (select 1) 200 1.5

2500MHz

SLOW (select 2) 500 0.75

FAST 100 0.75

SLOW 10 6

SLOW (select 1) 20 5

500MHz

SLOW (select 2) 50 1.5

FAST 10 0.5

SLOW 11.25

SLOW (select 1) 0.2 6

10MHz

SLOW (select 2) 0.1 11

NOTE: In SLOW Gate Time mode (Gate switch set to SLOW), pressing the RESO key

scrolls the meter through SLOW, SLOW (Select1), and SLOW (Select 2) modes.

Sensitivity specifications

100mVrms (50MHz to 75MHz)Ch.A: 2500MHz range

50mVrms (76MHz to 2500MHz)

120mVrms (10M to 35MHz)

50mVrms (36M to 350MHz)

Ch.B: 500MHz range

120mVrms (351M to 450MHz)

Ch.C: 10MHz range, Period  50mVrms

Notes on sensitivity: The apparent sensitivity when feeding a signal into Ch.A may vary

considerably, particularly near 1GHz. The meter’s input impedance is a complex impedance,

whereas the output of most signal generators is calibrated for a 50Ωresistive load. This will

result in a terminal voltage different to that expected by the generator, and therefore a

different sensitivity.

381235 Ver. 1.5 3/01

Front Panel Description

1. Channel A input

2. Ch. B input

3. Ch. C input

4. LCD display 8-digits

5. AC adapter jack (side)

6. Resolution key

7. Relative mode key

8. Data Hold key

9. Power ON key

10. Record mode key

11. Call mode key

12. Range select switch

13. Power OFF key

14. Gate time selecter switch

15. Sensitivity key

NOTE: Battery compartment is on lower

rear of meter secured by two screws

Operation

RF Antennae and Measurement Probes

The female BNC input sockets on the top of the meter accept RF Antennae or Direct

Measurement Probes with BNC connectors. These are optionally available through Extech

Instruments. Connect the RF Antennae or Direct Probes before powering the meter. It is

recommended that only RF Antennae be used for frequencies greater than 500MHz for

the best sensitivity.

Frequency measurements

1. Press the Power ON key to power the meter. If the display does not indicate digits

check the batteries or the AC adapter. To power down press the Power OFF key

2. Slide the Range selector switch to desired measurement range. Note that for the best

accuracy and resolution, be sure to use the most appropriate range.

3. Apply the measurement signal to the input Channel A socket if the frequency of the

signal is between 500MHz and 2500MHz.

4. Apply the measurement signal to the input Channel B socket if the frequency of the

signal is between 10MHz and 500MHz.

5. Apply the measurement signal to the input Channel C socket if the frequency of the

signal is less than 10MHz.

6. Slide the Sensitivity selector switch(es) to the HIGH or LOW setting if the measured

signal is less than 10MHz.

7. Slide the Gate select switch to the FAST or SLOW setting depending upon the desired

resolution and sampling rate (refer to the specifications section). Note that if SLOW is

selected, pressing the RESO key (up to 3 times) scrolls through up to 3

resolution/sampling rate display combinations. Press the RESO key and observe the

LCD each time for the different resolution/sampling rate combinations. The LCD flashes

at the sampling rate selected.

8. The units for the 500/2500MHz ranges is MHz and the units for the 10HMz range is Hz.

381235 Ver. 1.5 3/01

Data Hold Mode

To freeze the most recent reading on the LCD, press the HOLD button once. The HOLD

icon will alternately appear on the LCD with the held reading. To release the reading and

return the meter to normal operation, press the HOLD key again.

Relative Mode Measurements

To display the difference between a stored reading and actual measurements, press the

REL key once. The reading at the time of the REL key-press will be stored in memory. All

subsequent displays will represent the difference between the stored reading and the

actual measurement. Press the REL key again to return to normal operation. Note that the

RELATIVE function cannot be accessed if the meter is in Data Hold or Data Record

modes.

Data Recording (Min/Max/Avg) Mode

The DATA RECORDING mode permits the maximum, minimum, and average readings to

be stored and recalled. To start recording data, press the RECORD key once and the R.C.

icon will appear on the right side of the LCD. After the measurement session, press the

CALL key to begin recalling the stored data.

The 1st CALL key press shows the maximum reading and the ‘Hi’ icon alternately.

The 2nd CALL key press shows the minimum reading and the ‘Lo’ icon alternately.

The 3rd CALL key press shows the average reading and the ‘A’ icon alternately. (The

Average reading will continue to update every 10 samples).

To return to normal operation, press the RECORD key again.

Period Measurements

Input the signal to Ch. C.

Slide the Range selector switch to the PERIOD position.

Period measurements are taken the same as frequency measurements.

The input frequency range for the PERIOD function is: 10Hz to 10MHz.

The display will show 5 digits with ‘S’ for millisecond or ‘uS’ for microsecond units of time.

The principle of the period display is a calculation which uses the measured frequency in

Hz. Refer to the following equations for the calculation the meter uses to display PERIOD:

Period (in milliseconds) = 1000ms / frequency (in Hz)

Period (in microseconds) = 1,000,000 uS / frequency (in Hz)

Auto Power OFF

If the meter is not used (keys pressed, switches moved) for approx. 30 mins. the meter will

automatically power itself down to preserve battery life.

Over Range Indication

The LCD will indicate –oL—and meter will emit an audible tone if one of the following

conditions are met:

a. Input signal exceeds 10MHz in 10MHz range

b. Input signal exceeds 500MHz in 500MHz range

c. Input signal = 0 (no input connected) for the PERIOD range.

381235 Ver. 1.5 3/01

Maintenance

Battery Replacement

Note: Remove the probes or antennae before replacing the battery

a. When the display reading begins blinking, the battery voltage has fallen to critical

levels and requires replacing.

b. Loosen the battery compartment screws (lower left side of the case back).

c. Replace the 4 ‘AA’ 1.5V batteries and replace the cover.

Cleaning

Caution: Use only a dry (or slightly damp) cloth to clean the plastic case.

Calibration and Repair Services

Extech offers complete repair and calibration services for all of the products we sell. For

periodic calibration, NIST certification or repair of any Extech product, call customer

service for details on services available. Extech recommends that calibration be performed

on an annual basis to insure calibration integrity.

Warranty

EXTECH INSTRUMENTS CORPORATION warrants this instrument to be free of defects in parts and

workmanship for one year from date of shipment (a six month limited warranty applies on sensors and

cables). If it should become necessary to return the instrument for service during or beyond the warranty

period, contact the Customer Service Department at (781) 890-7440 for authorization. A Return

Authorization (RA) number must be issued before any product is returned to Extech. The sender is

responsible for shipping charges, freight, insurance and proper packaging to prevent damage in transit.

This warranty does not apply to defects resulting from action of the user such as misuse, improper wiring,

operation outside of specification, improper maintenance or repair, or unauthorized modification. Extech

specifically disclaims any implied warranties or merchantability or fitness for a specific purpose and will not

be liable for any direct, indirect, incidental or consequential damages. Extech's total liability is limited to

repair or replacement of the product.

The warranty set forth above is inclusive and no other warranty, whether written or oral, is expressed or

implied.

((

Tech Support Hotlines

781-890-7440 ext. 200

[email protected]

www.extech.com

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