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Chapter 14 Probe Zero

Zeroing the Probe While In Use

The meter and probe are initially zeroed before the meter is

allowed to go into the measurement mode. If you determine that

significant drift may have occurred, it is simple to fine tune the

zero. See

Checking for Zero Drift on page 82

To zero the probe while in use...

1. Shield the probe using one of the methods described

Shielding the Probe

2. Press the

Auto Zero

key. The meter will correct for any

probe drift in about eight seconds. The meter will then

automatically return to the measurements screen.

Содержание 8718B

Страница 1: ...USER S GUIDE Model 8718B Electromagnetic Radiation Survey Meter P N 42983600 RevB narda Safety Test Solutions an communications company L3...

Страница 2: ...pod and used with an optional fiber optic link for enhanced accuracy in certain applications Getting Started with the Model 8718B It is important to become familiar with the Model 8718B before you use...

Страница 3: ...y Charger Power Supply Power Cord 230 volt chargers only Storage Case Probe Extension Cable Model 8744 04 Electric Field Attenuator Model 8713B User s Software CD ROM Computer Cable User s Guide Using...

Страница 4: ...ge the meter first connect the cable of the battery charger to the larger jack on the left side of the meter Make sure the plug is fully inserted into the jack Connect the power cord to the wall outle...

Страница 5: ...gh a tiny hole on the bottom of the meter The alarm sounds whenever the field strength exceeds the measurement range of the probe over ranges You can also set the meter to sound its alarm at a specifi...

Страница 6: ...access this connector Operation With a Computer To update probe calibration information or retrieve stored measurements you must connect your Model 8718B to a personal computer and use the User s Sof...

Страница 7: ...keys are used to turn the Model 8718B On and Off Function Keys Use the four function keys F1 F4 to select the options displayed on the bottom line of the display screen directly above the F1 F2 F3 an...

Страница 8: ...er than use the Esc key Auto Enables you to automatically zero the meter Zero and probe Help Displays a help screen that explains your options Test Turns on the built in low frequency and high Source...

Страница 9: ...8 Operating the Meter...

Страница 10: ...ment range to get greater sensitivity In contrast higher power probes give additional safety margins especially at microwave frequencies where field strength can change rapidly with a small change in...

Страница 11: ...leaks in densely packaged microwave systems Shaped Frequency Response Probes The goal in designing and manufacturing a traditional flat frequency response probe is to make the probe equally responsive...

Страница 12: ...pter cable for attachment to older style 8700 series probes with integral cables or 2 a 4 ft 1 2m long cable with a quick release connector on both ends for use with the 8700 D series probes The D ser...

Страница 13: ...Label Color Band to Indicate the Full Scale Measurement Range 20 mW cm2 probes do not have a colored band Calibration Label With Frequency Correction Factors Field Type E or H Full Scale Measurement R...

Страница 14: ...Getting Started Press the On power key The meter model serial and firmware version will be displayed briefly After a few seconds the Opening Menu Screen will appear To Make Measurements 1 Select the...

Страница 15: ...arked on the handle of the probe Probes with this additional detail stored in the meter are referred to as probes in memory Putting probes into memory has several advantages It makes it easier to sele...

Страница 16: ...yed on the second line of the screen If this is correct press Enter 5 A new screen will appear specifying probe model number serial number frequency range field type maximum measurement range and type...

Страница 17: ...ge forward and backward until you do Press the appropriate number key to select a probe model 6 A new screen will appear specifying probe model number frequency range field type maximum measurement ra...

Страница 18: ...f you get a message that the probe could not be zeroed the most likely causes are The probe is not connected properly Check the connector and retry The meter is set for a fiber optic input and you are...

Страница 19: ...correct for any drift in a few seconds Measurement Display Screens There are two display screen options The Main Measurement Display Screen The Alternate Measurement Display Screen Main Measurement Di...

Страница 20: ...X indicates the numeric value that is being applied A frequency displayed here indicates that the meter is applying a correction factor based on the stored calibration data for the specific probe in u...

Страница 21: ...quency The use of the Alternate Measurement Display Screen also introduces an automatic correction for probe frequency deviation for probes in memory The option to change display screens is only avail...

Страница 22: ...LATED FIELD STRENGTH Displays field strength in mW cm2 that has been calculated from the STD reading using the referenced standard and the indicated frequency PROBE FREQUENCY CORRECTION CF 1 00 indica...

Страница 23: ...ing Probe Correction Factors on page 24 6 From the Main Measurement Screen press F1 ALT to select the Alternate Measurement Display Screen To return to the Main Measurements Display Screen 1 From the...

Страница 24: ...graph automatically switches between three ranges 0 01 to 1 1 to 10 and 10 to 100 HIGH 1 to 100 MID 0 1 to 10 LOW 0 01 to 1 If you exceed the upper limit of either the MID or LOW range the bar graph w...

Страница 25: ...uire six checks three high frequency and three low frequency Using Probe Correction Factors All probes have a certain amount of frequency sensitivity Frequency sensitivity is the amount of deviation f...

Страница 26: ...frequency for which you want to correct readings Make sure you fill in all four positions If you make a mistake just enter more digits until correct For greater accuracy use the units that allow the...

Страница 27: ...the right of the decimal point If you make a mistake just enter more digits until correct For example to enter a correction factor of 1 22 simply enter 1 2 and then 2 while a correction factor of 0 9...

Страница 28: ...2 Press 7 PROBE A Screen will appear that shows the model number and basic characteristics of the probe The probe serial number is shown for probes selected from memory 3 Press F1 OK key to return to...

Страница 29: ...tion factor If you rotate the probe around its axis and use the mean value ellipse ratio can be eliminated as a source of uncertainty Isotropic response is the error that occurs when the probe is poin...

Страница 30: ...iate chapter of this guide for detailed instructions The following keys are used to move through the various menu options and to set measurement parameters Function Keys F1 F4 Most menu options are of...

Страница 31: ...sed for whole body averaging on or off 7 4 BAT LITE Check battery charge status and estimated time remaining Turn the back light on or off 12 5 UNITS Select from all appropriate units of measure i e m...

Страница 32: ...et the function keys for right or left handed operation Adjust the display contrast 15 3 CABLE FO Select between the standard probe cable input and the fiber optic receiver 16 4 LOCKOUT Lock the keypa...

Страница 33: ...standard cable input CANCEL Cancel making the selection and return to the previous menu CONT Continuous initiate logging for an undefined interval CLEAR Clear the memory of logged data CLR Clear the s...

Страница 34: ...selection OFF Off turn special mode off OK OK continue with the same setting ON On turn special mode on PAUSE Pause during data logging or time averaging QUIT Quit special mode and return to the stand...

Страница 35: ...Default Condition Alarms Last Used settings will be used Back Light OFF to conserve battery power Blank Out OFF display will be active Cable Fiber Optic Last Used input will be active Data Logging OFF...

Страница 36: ...it of Measure Last Used unit of measure will be in use if previous and current probe both have flat or shaped frequency response If current probe is shaped unit will be of STD If current probe is flat...

Страница 37: ...36 Operating the Meter...

Страница 38: ...cy response or a shaped frequency response The available units of measure for the various types of probes are Percent of Standard is the only unit of measure available for shaped fre quency response p...

Страница 39: ...creen will appear that offers the available units of measure for the probe in use 3 Press the number key on the keypad that matches the desired unit of measure For example pressing 1 selects mW cm2 as...

Страница 40: ...den equal in height to an average adult with distance marks equally spaced along its length Measurements are made alongside the storypole at each height and then mathematically averaged The height and...

Страница 41: ...curate than averaging a series of measurements It is anticipated that future updates of the major standards will reflect this automatic technique now that the survey equipment makes it practical To ma...

Страница 42: ...left side of the third line of the display The bar graph will be indicating the instantaneous field magnitude in real time The averaging interval will be shown on the right side of the third line whi...

Страница 43: ...nother spatially averaged measurement press F1 START again 12 To end spatial averaging altogether press F4 QUIT The meter will automatically return to the standard measurement screen If you had access...

Страница 44: ...ed by the computer Analog Output An analog voltage is continuously available for use with a Chart Recorder or A D converter Logging Data The 8718B has three logging modes to collect field strength mea...

Страница 45: ...ific intervals of time for a specific time period Each data point also has a time and date stamp Format for Logged Data A record contains a header and one or more data points Each record is identified...

Страница 46: ...ilable memory and the amount of memory already used The bar graph is a rough indicator of remaining memory capacity as a percentage of total capacity See Memory Capacity at the end of this chapter for...

Страница 47: ...hat you can later associate this survey number with the data points collected If you make a mistake press F2 CLR to clear the screen and enter a new survey number 3 Press F4 QUIT or F3 MENU if you cha...

Страница 48: ...LOG again to log the second data point It will automatically be assigned data point 002 providing that you had saved the first data point If you had elected to discard the first data point then this...

Страница 49: ...Menu Screen Mode 2 Logging To initiate Mode 2 logging a series of spatially averaged data points with a reference number assigned to each data point 1 From the main data logging screen press the numbe...

Страница 50: ...a constant rate of movement Keep your finger on the F1 key during this operation 7 Strive for an interval of about ten seconds between starting and stopping the timer The displayed value will flash a...

Страница 51: ...the second spatially averaged data point It will automatically be assigned data point 002 providing that you had saved the first data point If you had elected to discard the first data point then thi...

Страница 52: ...lly return to the logged measurements screen 17 To end logging altogether and return to the standard measurement screen press F4 QUIT To initiate logging again at a later point use the menu system to...

Страница 53: ...t logging rates 1 SEC 10 MIN 1 MIN 10 HR and 2 HR 4 Press the number on the numeric keypad 1 5 that corresponds to the desired logging rate 5 A new menu screen will appear The numeric keypad and the f...

Страница 54: ...meter to stop or the memory is filled press F4 CONT The meter will automatically return to the measurement screen with new options available for the function keys 8 Proceed to make measurements as nor...

Страница 55: ...Q U I T F1 F2 F3 F4 R E 10 A screen will appear requesting that you assign another two digit survey number to the new logging run Use the numeric keypad to enter the two digit number and then press F...

Страница 56: ...er there is sufficient available memory to perform the desired task If there is proceed with logging as described above 5 If you determine that there is insufficient memory to perform the desired task...

Страница 57: ...nd warning that the stored information will be lost 12 Press F1 CLEAR to clear the memory or F1 ABORT to return to the First Menu Screen without clearing the memory S E T T I N G S 1 C L O C K 4 R G T...

Страница 58: ...To make time averaged measurements 1 Access the menu system by pressing the function key that corresponds to the legend below MENU on the bottom line of the display 2 Press number 2 on the keypad to...

Страница 59: ...n selected and is currently active that selection will be flashing 3 Press the number on the numeric keypad 1 4 that corresponds to the desired averaging interval and the meter automatically returns t...

Страница 60: ...electromagnetic field At the lower frequencies the measurement techniques are very different See Low Frequency Measurements in the Applications Booklet 7 Press F1 START when you are ready to begin th...

Страница 61: ...ging again at a later point use the menu system to select TIME AVG from the First Menu Screen To temporarily pause during a time averaged measurement 1 To temporarily suspend time averaging press F3 P...

Страница 62: ...he averaging interval 1 To change the averaging interval once the current measurement interval has been completed or stopped press F4 QUIT To initiate a new time averaging interval use the menu system...

Страница 63: ...ess F4 SAVE The meter will automatically return to the measurement screen 5 If the probe used is a probe in memory the frequency that you have set will be displayed on the right side of the third line...

Страница 64: ...atically shut off Mode 1 averaging if it is on 4 A new screen will appear stating that averaging has been enabled in accordance with a specific standard 5 Press F3 CANCEL to return to the initial time...

Страница 65: ...end of the averaging interval the meter will show the time averaged value on the second line of the display and the maximum value on the third line of the display The bar graph will be indicating the...

Страница 66: ...rth line of the display To resume time averaging and complete the measurement press F1 START 2 You may continue to pause and start the averaging as many times as needed The time interval determined by...

Страница 67: ...he current measurement interval has been completed or stopped press F2 CLR if the averaged value is displayed 2 Once the meter is displaying real time values the frequency menu is accessed by pressing...

Страница 68: ...em by pressing the function key that corresponds to the legend below MENU on the bottom line of the display 2 Press 8 NEXT to go to the Second Menu Screen 3 Press 5 ALARM to access the alarm menu A ne...

Страница 69: ...sound its alarm at 5 mW cm2 when using a Model 8721D probe which has a full scale measurement range of 20 mW cm2 set the alarm threshold to 25 3 If you want to turn the variable tone alarm on or off...

Страница 70: ...larm on the previous page 3 When you are satisfied with all the alarm settings press ENTER and the meter will return to the measurement screen Note The fixed and vari able tone alarms op erate indepen...

Страница 71: ...70 Operating the Meter...

Страница 72: ...e Measurement Display Screen on page 20 Time averaged measurements are made to conform to the referenced standard at the specified frequency Checking or Changing the Standard To determine which standa...

Страница 73: ...ng this standard as a reference without change To change the standard or tier that the 8718B references 6 Press F4 STNDS A new menu screen will automatically appear that lists several major internatio...

Страница 74: ...e standard and the selected tier are shown with two options available for the function keys 13 Press F1 OK to begin using this standard and tier as a reference 14 Alternately press F4 STNDS to select...

Страница 75: ...74 Operating the Meter...

Страница 76: ...han the meter circuits and significantly reduces operating time between battery charges Controlling the Back Light To turn the back light on or off 1 Access the menu system by pressing the function ke...

Страница 77: ...ed Checking Battery Status To check the battery status 1 Access the menu system by pressing the function key that corresponds to the legend below MENU on the bottom line of the display 2 Press 4 to se...

Страница 78: ...es It is a characteristic of these batteries to get a large voltage increase with only a brief charging period if one starts with a battery that is completely discharged However under such conditions...

Страница 79: ...78 Operating the Meter...

Страница 80: ...if the meter is left unattended during a long data logging session Keypad Lockout To lock the keypad 1 Access the menu system by pressing the function key that corresponds to the legend below MENU on...

Страница 81: ...2 Press number 8 NEXT to select the Second Menu Screen 3 Press 7 to select BLANK 4 The meter will automatically return to the measurements mode but will be blank The keypad will also be locked Only th...

Страница 82: ...the diodes are not operated in a saturated mode to insure accuracy in multi signal conditions the survey system must be zeroed The Model 8718B establishes the zero reference as a small positive voltag...

Страница 83: ...d probes use thermocouples but the circuit requires lower gain than the electric field probes The other possible cause of zero drift can occur when a probe is subjected to a very high field level and...

Страница 84: ...quire only a few minutes to stabilize The thermo couple sensors used in microwave band and ultra broadband probes may require 15 20 minutes to stabilize Establishing a Zero Field It is important to ze...

Страница 85: ...t to move the probe while zeroing takes place On probes with low frequency test points you can create static which will give inaccurate results although this is less of a concern with the new 8700D se...

Страница 86: ...significant drift may have occurred it is simple to fine tune the zero See Checking for Zero Drift on page 82 To zero the probe while in use 1 Shield the probe using one of the methods described in S...

Страница 87: ...86 Operating the Meter...

Страница 88: ...ating at a different ambient temperature Clear the memory of logged data Set the function keys for right or left handed operation Adjust the contrast of the display Accessing the Settings Menu To acce...

Страница 89: ...Y 3 Press the Esc key to return to the First Menu Screen without making any changes To set the time 1 Press F1 SET The display will change to show four underscored lines where the new time must be ent...

Страница 90: ...in to return to the measurements screen Temperature Correction This feature is only used when the meter and probe are operating at significantly different ambient temperatures This situation can occur...

Страница 91: ...wing the procedure described in Accessing the Settings Menu 2 Press 2 to select TEMP A new screen will appear that shows the current mode The default mode is Auto Correct 3 Press F1 OK to continue wit...

Страница 92: ...current memory contents prior to clearing the memory you must connect the 8718B to your computer See Chapter 18 User s Software To clear the memory 1 Access the settings menu by following the procedu...

Страница 93: ...be certain that your thumb is in the correct location The START and LOG functions are always operated with the F1 key for right hand operation The 8718B allows you to change to left handed operation w...

Страница 94: ...r typical conditions The user can adjust the contrast to optimize visibility under specific lighting conditions To adjust the display contrast 1 Access the settings menu by following the procedure des...

Страница 95: ...9 with 0 for the lightest setting and 9 the darkest setting The contrast will change as soon as the numeric value is entered You may continue to experiment as many times as needed by entering a new va...

Страница 96: ...the components in the system meter fiber optic transmitter and probe are independently calibrated The fiber optic transmitter converts the analog DC voltage out of the probe amplifier to a series of...

Страница 97: ...ttery Charge Turns Battery Off Turns Power On LED Ona LED Off LED Off CAL 1 S2 NORM CAL 2 Tests Channel 1 Normal Operation Tests Channel 2 Meter mid scale Variable Level Above mid scale a The battery...

Страница 98: ...Esc to return to the measurements screen 5 Press F4 FO to change to the fiber optic receiver input The meter will return to the First Menu Screen Press Esc to return to the measurements screen To set...

Страница 99: ...y that the green LED is illuminated which signifies that the battery is adequately charged for operation If the LED fails to illuminate charge the transmitter overnight A full battery charge takes app...

Страница 100: ...level corresponds directly with the indication on the bar graph of the display Under normal conditions the bar graph is in the AUTO mode which results in the bar graph using three 10 dB ranges to cov...

Страница 101: ...0 mW cm2 1 50 volts Half Scale 10 0 mW cm2 3 00 volts Full Scale 10 1 mW cm2 0 03 volts 1 of Full Scale 50 mW cm2 1 50 volts Half Scale 100 mW cm2 3 00 volts Full Scale 100 mW cm2 4 2 4 5 volts RANGE...

Страница 102: ...d to provide meter diagnostics and to load firmware updates into the meter The User s Software for the Model 8718B is supplied on a compact disk It should be permanently installed on the hard drive of...

Страница 103: ...created Starting and Exiting the 8718B User s Program To start the 8718B User s Program 1 Click on Programs from the Start menu in Microsoft Windows 2 Select the 8718B User s Software icon The Main M...

Страница 104: ...103 Chapter 18 User s Software Main Menu Screen...

Страница 105: ...et to the same as the User s Software The meter setting will be the same as the last time the meter was used 8 Check that the CTS indicator on the computer screen has turned red and the status has cha...

Страница 106: ...number that have been installed in your Model 8718B A small box just below the table lists the total number of installed probes To simply view the details of any installed probe proceed to Viewing In...

Страница 107: ...highlighting the box to the right of legend Enter Cal Date This date is shown on the handle of the probe Hit the Tab key on the computer 5 The Calibration Due date is automatically calculated as one y...

Страница 108: ...107 Chapter 18 User s Software Probe Installation Screen...

Страница 109: ...er and the serial number of the probe just installed will now appear in the table of Installed Probes 11 To leave the Probe Installation window and return to the main menu click the Close button Remov...

Страница 110: ...ata and its location on your hard drive Make note of this information and click OK File Format for Survey Data Data files can have one of three forms identified by the suffix in the file name 1 The fi...

Страница 111: ...le you want to view from the list of files by either double clicking on it or highlighting it and choosing OK 3 A new window labeled Logged Survey Data will appear The file name will be shown to the r...

Страница 112: ...111 Chapter 18 User s Software Logged Survey Data Screen...

Страница 113: ...ar graph on the right side of the screen shows the same data listed in the table The title of the bar graph is Logged Data for Mode 1 data Spatial Average Max for Mode 2 data and Continuous Log for Mo...

Страница 114: ...table on the left Downloaded survey files are stored in a subdirectory labeled Svy You can change drives select which types of files are listed or change directories from this box 2 Select the data fi...

Страница 115: ...le from the Export menu A dialog box will appear titled Make Tab txt File The file selected to be exported drive will be listed in the table on the left The default directory for exported survey files...

Страница 116: ...ssword protected Diagnostics menu of the User s Software can be used if you experience a problem with your 8718B Narda may be able to troubleshoot the problem using the built in diagnostic tools of th...

Страница 117: ...click OK to continue or click Cancel to abort the update process 6 Enter the password obtained from Narda and click OK 7 Read the description of the three meter models Click Yes to update a Model 871...

Страница 118: ...the checksum would be D and 2 the decimal hex conversion of 210 An equivalent calculation is to convert the sum to Hex and transmit the two lowest digits The Hex of 1234 is 4D2 therefore the digits to...

Страница 119: ...es units 6 bytes READ MAX Command Characters Function I Communications Protocol A Ground Rules 1 CS two digit checksum 2 ASCII Hex characters NOTE The is NOT included in the checksum calculation 2 CR...

Страница 120: ...CR 3 3E 46 30 01 34 32 37 31 32 41 37 0D M000CSCR M000DDCR 3E 4D 30 30 30 44 44 0D V000CSCR V000E6CR 3E 56 30 30 30 45 36 0D Auto Zero ASCII Hex Read Clock ASCII Hex Where Correction Factor ASCII Hex...

Страница 121: ...to 4 for maximum display averaging Example to set minimum display averaging 4 1 D100D5CR 3E 44 31 30 30 44 35 0D P000CSCR P000EOCR 3E 50 30 30 30 45 30 0D L000CSCR L000DCCR 3E 4C 30 30 30 44 43 0D H00...

Страница 122: ...cteristics of the probe used Probe Functional Description The probe senses the electromagnetic fields and develops a signal for transmission to the meter The probe has an isotropic sensing pattern so...

Страница 123: ...meter of approximately 0 75 mW cm2 3 dB b Low Frequency Test Source An external test point provides a 10 kHz nominal signal at the unit and test points on the probe to excite each low frequency eleme...

Страница 124: ...123 Appendix B Theory of Operation Model 8718B Functional Block Diagram...

Страница 125: ...am memory U11 The LCD module receives input from the data bus along with a contrast control input from U8 through U2A R2 and R21 The LCD back light control is provided from P O Q4 which is controlled...

Страница 126: ...All probes are internally coated with a thin film high resistive coating The film is on the order of 0 5 M per square inch and provides a shield against electrostatic charges All 8700 series probes u...

Страница 127: ...B meter Models include the Model 8741D that has a flat frequency response and the x8722D series that have shaped frequency response characteristics In the lower frequency region below 1500 MHz a dipol...

Страница 128: ...s The major advantage is the greatly reduced interaction between the meter and probe the human body making the measurements and the RF field The Model 8782D uses an active antenna design to accurately...

Страница 129: ...128 Appendices...

Страница 130: ...f detergent or solvent Calibration The Model 8718B is calibrated before it is shipped Narda recommends that the Model 8718B be calibrated every two years Narda will perform this calibration for a nomi...

Страница 131: ...0 Insulated Tripod Handle 21797900 Optional Accessory Tripod Adapter 32595900 Optional Accessory Battery Charger and Line Cord Options The Model 8718B contains a rechargeable battery The meter is supp...

Страница 132: ...h applicable federal state or local environmental regulations Narda maintains a rechargeable battery management program in keeping with its highly proactive policy on environmental protection and cons...

Страница 133: ...132 Appendices...

Страница 134: ...king 80 Display Screens measurement Alternate 20 Main 19 Fiber Optic Link operation with Application 95 Controls and Indicators 95 Setting the Meter 96 System Checks 98 Keypad Function Keys 6 Numeric...

Страница 135: ...d Clock setting the 88 Display Contrast adjusting 93 Function Keys right or left handed 92 Memory clearing the 91 Menu accessing the 87 Temperature Correction 89 Theory of Operation Meter functional d...

Страница 136: ...disassembled modified physically or electrically damaged or any product that has been subjected to conditions exceeding the applicable specifications or ratings Narda STS shall not be liable for any d...

Страница 137: ...ge NY 11788 Tel 1 631 231 1700 Fax 1 631 231 1711 E Mail NardaSTS L 3COM com www narda sts com GERMANY Sandwiesenstrasse 7 D 72793 Pfullingen Tel 49 7121 9732 777 Fax 49 7121 9732 790 E Mail support n...

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