KEI 7158 Operating 电路图.pdf

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1、Model 7158 low Current Scanner Card Instruction Manual Contains Operating and Servicing Information RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 Model 7158 Low Current Scanner Card Instruction Manual 0 1987, Keithley Instruments, Inc. Test Instrumentation Group All rights reserved. Cleveland, Ohi

2、o, U.S.A. June 1990, Second Printing Document Number: 7158-901-01 Rev. B RadioFans.CN 收音机爱 好者资料库 SAFETY PRECAUTIONS The following safety precautions should be observed before using this product and any associated instrumentation. Although 6ome instruments and accessories would normally be used with

3、non-hazardous voltages, there are situations where hazardous conditions may be present. This product is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety precautions required to avoid possible injury. Read the operating information carefully before

4、us- ing the product. Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector jacks or test fixtures. The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30V RMS, 42.4V peak, or 60VDC are

5、 present. A good safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring. Before operating an instrument, make sure the line cord is connected to a properly grounded power receptacle. Inspect the connecting cables, test leads, and jumpers for possible w

6、ear, cracks, or breaks before each we. For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under test. ALWAYS re- move power from the entire test system and discharge any capacitors be- fore: connecting or disconnecting cables or

7、jumpers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers. Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth) ground. Always make measurements with dry hands while stan

8、ding on a dry, insulated surface capable of withstanding the voltage being measured. Do not exceed the maximum signal levels of the instruments and awes- series, as defined in the specifications and operating information, and as shown on the instrument or test fixture rear panel, or switching card.

9、Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance limited sources. NEVER connect switching cards directly to AC main. When connecting sources to switch- ing cards, install protective devices to limit fault current and voltage to the card

10、. When fuses are used in a product, replace with same type and rating for continued protection against fire hazard. Chassis connections must only be used as shield connections for measur- ing circuits, NOT as safety earth ground connections. If you are using a test fixture, keep the lid closed while

11、 power is applied to the device under test. Safe operation requires the use of a lid interlock. If a screw is present on the test fixture, connect it to safety earth ground using #18 AWG or larger wire. The f symbol on an instrument or accessory indicates that 1OOOV or more may be present on the ter

12、minals. Refer to the product manual for de- tailed operating information. Instrumentation and accessories should not be connected to humans Maintenance should be performed by qualified service personnel. Before performing any maintenance, disconnect the line cord and all test cables. SPECIFICATIONS

13、MODEL 7158 LOW CURRENT SCANNER CARD CHANNBLS PER CARD: 10 CONTACT CONFIGURATION: Single pole. When a channel is open, sign81 HI is con- nected to signal LO. Signal LO is common for ail 10 channels and aulput. CONNIXTOR TYPE; BNC RELAY DRIVE CURRENT: lOOmA per card typical. MAXIMUM SIGNAL LEVEL; lOOm

14、A, 3OV, peak (resistive load) 368 BANDWImHz lM 10 closures (at maximum signal level) CONTACT RESISTANCE: Xl to rated life CONTACT POTBNTIALr 20, Model 4801 Low Noise Cable ACCBSSORY AVAILABLG; Model 4804 t WlS Scanner 7158 Ch. No. Ch. No. 001 002 003 004 005 006 0”: 009 010 011 012 013 014 015 016 0

15、17 018 019 020 3 : 5 5 6 6 7 7 i ; 10 10 I Card 2 20 de1 7064 Scanner Ch. No. 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 lnels 7064 Ch. No. 1 2 3 4 : i 9 10 11 12 13 14 15 16 17 :i 20 Next, consider a mix of a lo-channel card Model 7l58), a 20-channel card (Model

16、 7064), and a matrix card (Mode 7052) in a Model 706 scan- ner mainframe. Since a matrix card is present, the scanner is set to matrix (O-pole) mode. The scanner crosspoints and card channel assignments for a master scanner are shown in Table 2-3. Table 2-3. Example Channel Assignments in Matrix (O-

17、Pole Mode) lard 1 - Model 7l.V Card 2 - Model 7064 10 cha 706 :rosspoi”l 001,l 002,l 003,l 004,l 005,l 001,2 002.2 003,2 004,2 005.2 l”“l t c els 7158 :h. No. : 3 4 5 ; 8 9 10 20 chal 706 Crosspoints 006.1 007.3 006.1 006,3 007,l 0073 007,l 006,3 008.1 ow,3 008,l 0063 009,l 007,3 009,l 006,3 010.1 0

18、07,3 010.1 006,3 006.2 007,3 006,2 006,3 007,2 007,3 00 x2 006,3 008,2 0073 008,2 006,3 009,2 007.3 009,2 006,3 010,2 007,3 010.2 006,3 R”l i ( els 7064 :h. No. : 3 t 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 kd 3 - h Colum”! 706 Zrosspoinl 011.1 011,2 011,3 011,4 012,l 012,2 ol2,3 ol2,4 013.1 ol3.2

19、013.3 013.4 014,l 014.2 014,3 014,4 015.1 015,2 015,3 015,4 Id 7052 , 4 rows _ 7052 :ohmn, Row _ ;*; 113 1.4 2,1 E 214 3.1 3.2 3.3 3.4 4.1 4.2 4,3 4,4 t: ;,3 5,4 When using 20.channel cards in matrix mode, two crosspoints must be closed for each of the card channels. in general, the rules for choosi

20、ng different scanner pole modes are: matrix (O-pole) - If a matrix card is present. l-pole - If a 20-channel card is present, but no matrix card. 2-p 8 9 10 Table 2-7. Scanner Control of Model 7158 Matrlx (O-Pole) Mode 1 Card 1 Card 6 icanner :h. 26, 1 27, 1 28, 1 29, 1 30, 1 26, 2 27, 2 28, 2 29, 2

21、 3a 706 06, 1 11, 1 07. 1 12. 1 08, 1 13, 1 09, 1 14, 1 10, 1 15, 1 06, 2 11, 2 07, 2 12, 2 08, 2 13, 2 Card 7 Scanner Ch. No. 31, 1 32, 1 33, 1 34, 1 35, 1 31, 2 32, 2 33, 2 34, 2 35, 2 706 Card 8 kanner Ch. No. 36, 1 37 1 38, 1 39, 1 40, 1 36, 2 37, 2 38, 2 39, 2 40, 706 Card 9 Scanner Ch. No. 41,

22、 1 42, 1 43, 1 44 1 45, 1 41, 2 42, 2 43, 2 44 2 45, 2 706 I Card 10 Scanner Ch. No. 46, 1 47. 1 4% 1 49, 1 50, 1 46, 2 47, 2 Ia 2 49, 2 50, 2 706 7158 Ch. No. : 3 4 5 r+ 8 9 10 n.58 :h. No. 1 2 3 4 5 6 7 8 9 10 17 2.5.2 Operation Notes 1. Extreme environmental conditions can cause the offset curren

23、t to exceed the 1pA specification. If the card has been exposed to high humidity and/or temperahue (for example during shipping), stabilize the board within the specified environmental limits for 24 hours. 2. When a channel is opened or closed, there is a charge transfer in the picocoulomb range. Th

24、is is because of the mechanical release or closure of the contacts, the contact to coil capacitance, and the stray capacitance between signal and relay drive lines. The charge transfer causes a current pulse. The effect on the signal depends on the magnitude of the source being measured. 3. Each rel

25、ay on the Model 7158 draws lOmA. For current switching, there are either ten or eleven relays energized with any combination of open and closed channels. The maximum current draw of one card from the mainframe power supply is 1lOmA. (For voltage swit- ching, there are between zero and eleven relays

26、energized for any open/closed channel combination.) There are no restrictions on the maximum number of simultaneous channel closures unless relays from other card types are energized at the same time. 4. System response is affected by cable capacitance. This should be con- sidered when the sources a

27、re connected to the scanner. Use of a feed- back ammeter (or an electrometer in the FAST mode) for currents below 10A is recommended to increase measurement speed and decrease the effects of cable capacitance. 5. Power Limits - To prevent overheating or damage to the relay con- tacts, never exceed t

28、he signal level specifications of the card. Max- imum switched and carry current and voltage levels are lOOmA, 30V. The card can switch low power AC (typical bandwidth up to lMHz). Maximum switched and carry current and voltage levels are lOOmA, 3OV, peak (resistive loads). 6. Switching Speed -Relay

29、 actuation time is lmsec maximum plus the mainframe programming time. Maximum relay switching rate is 100 cycles per second (10msec). This is the maximum rate of the scan- ner mainframe. For extended relay life, use low power or cold swit- ching (turn on sources after the channel is closed). 2.6 APP

30、LICATIONS The Model 7158 can be used in a variety of applications to switch low 18 current levels. Typical appltcations include those where sourcing voltage and measuring current are required, such as: ? Leakage currents (e.g. capacitor, FET gate) ? PCB test coupons ? Materials research and characte

31、rization ? Semiconductor sub-threshold current Voltage applications include those where the Model 7158 can be used to switch a single-pole of low voltage sources. (Refer to the application example that follows.) When measuring low currents, the following sources of noise current should be considered

32、: ? Triboelectric currents are caused by friction behveen a conductor and insulator when a coax cable flexes due to vibration or temperature fluctuation. To minimize, use low noise cables and tie down to a rigid surface. ? Piezoelechic currents are caused by mechanical stress to the insulating mater

33、ials of connectors. Remove the stress from the insulators and use material with low piezoelectric effects to minimize. ? Electrochemical effects generate current between PCB conductors due to contamination of the card surface. To minimize, handle the card by the edges only and follow the cleaning in

34、structions in paragraph 3.2. For a specific application, consider measuring capacitor leakage cur- rent to calculate insulation resistance. The amount of leakage current depends on the capacitor dielectric material as well as the applied voltage. The schematic of Figure 2-5 shows a Model 705517056 c

35、ard on the source side, but a Model 7158 could be used in its voltage configma- tion when the test voltage does not exceed 3OV. The configuration shown is the direct method of measuring leakage currents: a feedback type picoammeter in series with the capacitor under test. This test is fully explaine

36、d (including controlling software 19 and test fixture construction) in Application Note #l20, “Capacitor Leakage Measurements”, NOTE The indirect method, with a voltmeter reading the voltage drop across a resistor in series with the capacitor, is recommended for capacitor values above l to maintain

37、stability and noise performance. The instrument setup is shown in Figure 2-6. For clarity, only four chan- nels are shown. Obviously, all ten channels are available for testing purposes. r- -7-1 Figure 2-5. Capacitor Leakage Schematic 20 Figure 2-6. Capacitor Leakage Instrument Setup The internal vo

38、ltage source of a Model 617 electrometer stagger charges the capacitors when the corresponding channels are closed on a Model 7056 general purpose card. (At this time, the signal HI to Lo relay on 21 the Model 7158 is closed, completing the circuit.) Resistor Rl is needed to limit current in case th

39、e capacitor is shorted and it also helps reduce noise. After each capacitor is fully charged (usually 10 times RlC), the Model 7I58 channel is programmed to close. This switches in the Model 617 for reading current or resistance (V/I mode). Once the Model 617 has settled and the measurement is taken

40、, the Model 7l58 channel is opened and the signal HI to LO relay closes to shunt the current to ground. Then the Model 7056 channel is opened to avoid a current surge through the electrometer and resistors Rl and R2 bleed off the capacitor charge. With this two-card configuration, the capacitors hav

41、e equal soak times. This is important when comparing low leakage levels (picoamps). Having equivalent soak times is not as critical at higher leakage levels (e.g. the nanoamp range of tantalum capacitors). In this case, the one- card configuration shown in Figure 2-7 is sufficient. Since the settlin

42、g time of the Model 617 is less when measuring higher currents, the chan- nels can be switched faster. 22 - - - - SHlELDED TEST FIXTURE SHlELDED TEST FIXTURE Figure 2-7. Maasurlng Leakages wlth One Card Figure 2-7. Maasurlng Leakages wlth One Card 23/24 SECTION 3 SERVICING INFORMATION 3.1 INTRODUCTI

43、ON This section describes tests for verifying the performance of the Model 7158. Perform these tests in an environment of 18C to 28C up to 70% RH. Because of the low signal levels measured in these tests, the test cables should be kept as still as possible to help minimize noise. Recommended mainten

44、ance includes inspection of the card and the card edge connector to ensure good electrical contact. 3.2 HANDLING AND CLEANING Because of the high impedance of the board, take special care when handling and using to prevent degradation of performance. Handle the board by the edges to avoid contaminat

45、ing it with dirt, body oil, etc. CMOS and other high-impedance devices are subject to possible static discharge damage because of the high impedance levels involved. When handling such devices (indicated by * in the parts list), use the follow- ing precautions: 1. Such devices should be transported

46、and handled onl in containers specially designed to prevent or dissipate static bull -up. Typically, ,J these devices will be received in anti-static containers of plastic or foam. Keep these parts in their original containers until ready for installation. 2. Remove the devices from their protective

47、 containers only at a grounded work station. Also, ground yourself with a suita IT roperly le wrwt strap. 25 3. Handle the devices only by the body; do not touch the pins. 4. Any printed circuit board into which the device is to be inserted must also be grounded to the bench or table. 5. Use only an

48、ti-static de-soldering tools and grounded-tip soldering irons. Before cleaning the board, remove the front and rear relay covers. Clean the board with cotton swabs or a soft brush saturated with an uncon- taminated solvent, .such as Freon TMS or TE. After the solvent has been applied and is still li

49、quid, blow-dry the board with dry-pumped nitrogen gas. 3.3 RELAY REPLACEMENT If you have determined that a relay is defective, use the following pro- cedure to replace it: 1. Remove the screws that secure the appropriate relay cover and remove the cover. 2. Unsolder the defective relay and clean the card holes with a desolder- ing tool or wick. Solder in a replacement relay. 3. Clean the car