KEI 228A REF GUIDE 电路图.pdf

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1、RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 Model 228A Voltage/Current Source All references to the Model 228 apply also to the Model 228A 01985, Keithley Instruments, Inc. All rights reserved. Cleveland, Ohio, U.S.A. Document Number: 228A.904.01 RadioFans.CN 收音机爱 好者资料库 WARRANTY Keithley Instrum

2、ents, Inc. warrants this product to be fox from defects in magnaI lerminals are Installation Category I and must nor be connected to mains. Do not connect switching cards direcdy 10 unlimited power circuits They are intended to be used with impedance limited sources. NEVER connect swiiching cards di

3、rectly 10 AC mains. When con- necting sources to switching cards. install protective devices 10 lim- it fault currem and voltage to rhe card. Before operating an ins,rumen,. make sure rhe line cord is conncct- ed to a properly grounded power receptacle. lnrpcct the connccim cables, test leads. and j

4、umpers for possible wear. cracks. or breaks before each use. For maximum safety, do not touch the product, test cables. or an) orher instruments while power is applied IO the circuil under :es,. ALWAYS remove power from ihe entire lest system and discharge any capacitors before: connccring or discon

5、necting cables or jump- ers, installing or removing switching cards. or making imemal changes, such as installing or removmgumpers. Do not louch any objea rhat could provide a currcm path to the common side of the circuit under rest or power line (earth) sround. Always make measurements wirh dry han

6、ds while rrandinp on a dry. insulated surface capable of wirhstanding he voltage being measured. The instrument and accessories must be used in accordance with its specifications and operating instructions or the safety of the equip- ment may be impaired. Do not exceed the maximum signal levels of t

7、he instruments and ac- cessorics, as defined in the specifications and operating informa- tion, and as shown on the instrument or test fixture panels, or switching card. When fuses are used in a product, replace with same rype and rating for continued protection against fire hazaid. Chassis connecti

8、ons must only be used as shield connections for measuring circuits, NOT as safety earth ground connections. If you are using a rest fixture. keep the lid closed while power is ap- plied to the device under test. Safe operation requires the use of a lid interlock. lfa 0, mew is present, connect it to

9、 safety earth ground using the wire recommended in the user documentation. The h symbol on an instrument indicates that the user should re- fer to the operaring instructions located in the manual. Then symbol on an instrument shows that it can source or mea- sure 1000 volts or more. including the co

10、mbined effect of normal and common mode voltages. Use standard safety precautions IO avoid personal contact with these voltages. The WARNING heading in a manual explains dangers that might result in personal injury or death. Always read the associated infor- mation very carefully before performing t

11、he indicated procedure. The CAUTION heading in a manual explains hazards that could damage the instrument. Such damage may invalidate the warranty. Insrmmentation and accessories shall not be connected to humans. Before performing any maintenance, disconnect the line cord and all test cables. To mai

12、ntain protection from electric shock and fire, replacement components in mains circuils, including the power transformer, test leads, and input jacks, must be purchased from Keithley lnstru- merits. Standard fuses, with applicable national safely approvals, may be used if the rating and type are the

13、 same. Other componenrs that are not safety related may be purchased from other suppliers as long as they are equivalent to the original component. (Note that se- lected pans should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product.) If you are unsu

14、re about the applicability of a replacement component, call a Keithley instruments office for information. To clean an instrument, use a damp cloth or mild, water based cleaner. Clean the exterior of the instrument only. Do not apply cleaner directly to he instrument or allow liquids to enter or spi

15、ll on the instrument. Products that consist of a circuit board with no case or chassis (e.g., data acquisition board for installation inm a computer) should never require cleaning if handled according to in- structions. If the board becomes contaminated and operation is af- fected, the board should

16、be returned to the factory for proper cleaning/servicing. Rev. 10199 CHAPTER 1 Introduction This booklet has been written to help the user understand the operation and specifications of the Model 228 Voltage/Current Source. The chapters in this booklet have been written to aid the user in some appli

17、cations. Terms relating to the V/I source such as: stability, line regulation, load regulation and sensing are defined in the glossary. For a complete explana- tion of the instrument including front panel controls and IEEE-468 bus operation refer to the Model 228 Instruction Manual (Document Number

18、228-901-01). The Model 228 is a power supply that can source OT sink electrical power. These unique features set it apart from ordinary power supplies. Actually, because of the Model 228s precision and wide dynamic range, the term SOURCE is used to differentiate it from or- dinary power supplies. Mo

19、st power supplies do what the name implies they supply power- usually voltage or current. The Model 228 is capable of precise control of voltage or current while sourcing or sinking power. In general, instruments that are defined as power sources supply electrical power to a con- nected load. Some p

20、ower sources can also act as a load for a” external source. This is generally known as sinking power. There are numerous applications for a” instrument that can sink power as well as supply power. For example, the Model 228 can charge then discharge a battery at a controlled rate. There are three fe

21、atures that differentiate the Model 228 from power supplies: 1. Multiple Ranges 2. Four Quadrant Operation 3. Constant Voltage/Co”sta”t Current Glossary Accuracy-Accuracy is defined as how close the actual output value reflects the programmed value. Display monitor accuracy is defined as how close t

22、he display monitor reflects the actual output value. Auto Cal-The A/D converter in the Model 228 measures various gains and offsets within the instrument. With this information, the microprocessor calculates calibration fac- tors which it uses when programming the output. Power on, Program 6 and Pro

23、gram 9 all start the Auto Cal sequence. Battery Back Up-Values programmed into the 100 step memory are saved even when the AC power is turned off. This is possible because the values are stored in CMOS memory which is powered by a rechargeable battery. Common Mode Voltage-Common mode voltage is the

24、potential difference between “earth ground and normally common” output terminal of the Model 228. This voltage is normally generated when connecting two power supplies in series. Compliance-Compliance is defined as the extent to which an output parameter (voltage or current) deviates from the progra

25、mmed value without compromise of the output parameter. e.g. For constant voltage operation, current control yields to voltage control as long as the actual output current is within the range of +ISEING (the program- med setting) to -IsETTING (the compliance setting). Outside this range, the current

26、control circuit attempts to take control of the output away from the voltage control circuit. Constant Voltage/Current-A constant current source can force current through a device under test almost independently of the load resistance. A constant voltage source can deliver a voltage across a device

27、almost independently of the load resistance. Current Monitor-The Model 228 output current is sensed internally and converted to the *lV full scale voltage. This voltage is routed to the A/D converter and circuitry but, also is available to the user via the current monitor output terminals. Dwell Tim

28、e-Dwell time is the time spent on a specific memory location. Dwell time is used in the Single Step, Single Cycle and Continuous memory control modes. The range of dwell time is 20msec to 1000sec. Floating-Floating is the term used to describe a condition where a common mode voltage exists between e

29、arth ground and the instrument or conductor of interest. Four Quadrant Operation-In four quadrant operation, voltage or current can be either positive or negative thus, four combinations are possible. Positive polarity of voltage and current is defined as “source quadrants”, where power is delivered

30、 from the Model 228 to the users load. Opposite polarity of voltage and current (+V, -I) or (-V, +I) is de- fined as “sink quadrants”, where power from the user is dissipated in the Model 228. Impedance-The effect of R, L, or C in series or parallel with the output. This causes the output voltage or

31、 current to vary slightly when load changes occur. Load-The device to which power is delivered. Load Line-The load line is the operating line on the V vs I graph for a particular load. Load Regulation-Load regulation is the ability of the Model 228 to keep the output voltage or current constant when

32、 the load changes. Modulation (External)-External modulation is a low frequency (DC to 600H.z) low voltage (rlOV) signal that is supplied by the user and is superimposed on the output signal of the Model 228. 2 Operate-Operate programs the output to the user selected values. Standby programs the out

33、put to OV, OA. During operate, the two displays show actual measured values of voltage and current. During standby, the programmed settings are displayed. Quick Disconnect Board-An output board that contains the OUTPUT, SENSE, EXTERNAL MODULATION and CURRENT MONITOR terminals. This board fits into t

34、he re- cessed slot on the rear panel of the Model 228. Response Time-Response time is the time the Model 228 microprocessor takes to respond to a signal on the External Trigger input. Response time is measured from trigger in- put until the output has change 99% of the difference between the old mem

35、ory step and the new memory step. A range change, polarity change or change between voltage and current extends the response time. Self Test-During the power on sequence the Model 228 tests memory (RAM and ROM), the AID converter control circuitry and power supplies. During operation, the Model 228

36、monitors temperatures, power supplies and the AID converter. If an error is discovered, the Model 228 attempts to protect the user and itself. Sense (Local and Remote)-Remote sensing maintains regulation at the load instead of the output terminals of the Model 228 therefore, compensating for the tes

37、t leads IR voltage drop. Local sensing maintains regulation at the output terminals of the Model 228. Source (Vice Sink-Source is a condition where in the Model 228 delivers power to the users load. Stability-Stability is the ability to keep from changing. Trigger IN most power supplies would be dam

38、aged if external voltages or currents are forced upon them. Figure 12 is a suggested protection circuit for the external power supply. The two protection diodes in the circuit protect most supplies in the event one of the following situations occur. 1. Incorrect Model 228 polarity. 2. Improper power

39、 on sequence (Model 228 before external supply), 3. The Model 228 is programmed for excessive voltage. 23 MODEL 228 PROTECTION FOR USERS SUPPLY Figure 12. Power Supply Protection Circuit Model 228 Extended Voltage and Current The Model 228 has several ranges that can be selected to suit a particular

40、 application. The most power a Model 228 can produce is 1OOW. This level of power can be obtained by 1OOV at 1A or 1OV at 10A. In general, this power is enough for most applications. Sometimes however, a higher voltage or a higher current that is outside of the Model 228 specifications is required.

41、In these situations the Model 228 can be connected to another Model 228 for higher output of voltage or current. NOTE Connecting multiple Model 228s in series or parallel does not increase the sink capability. Instead, it increases the voltage or current source capability. 24 The highest amount of v

42、oltage possible from multiple Mode1 228s is 200V. This is due to the common mode voltage specification of 1OOV. The common mode voltage of 1OOV must not be exceeded on either instrument. Figure 13 shows the method of connecting two Model 228s in series to obtain a higher voltage. Figure 14 shows the

43、 recommended method of con- necting more than two Model 228s in series to obtain a higher voltage. In Figure 14 there are three Model 228s. The voltage obtained is not 300V. The maximum is ZOOV. For exam- ple, on the lOV, 1OA range, 30V at 10A can be achieved Figure 13. Two Model 228s in Series 25 N

44、OTE MAXlMUM COMMON MODE VOLTAGE IS 100”. DIODES MUST SE RATED FOR TWO TIMES THE MAXlMUM VOLTAGE AND ONE TIME THE MAXIMUM CURRENT. Figure 14. Multiple Model 228s in Series Higher current can be obtained by connecting multiple Model 228s in parallel. Refer to Figure 15. Two supplies can be connected i

45、n parallel for higher current without any additional pro- tection circuitry. If more than two supplies are connected in parallel additional protection circuitry is required as shown in Figure 16. The diodes allow the supplies to output current but not to sink current. In Figures 15 and 16 the suppli

46、es are set for remote sense. The amount of current is limited to the number of supplies connected in parallel. Each Model 228 can deliver up to 1OA on the lOV, 10A range. Each additional Model 228 connected in parallel increases current capability another 10A. For example, if three Model 228s are co

47、n- nected in parallel as shown in Figure 16, current capability is increased to 30A. This rating is on the lOV, 1OA range. The increase in current capacity applies to all the ranges of the Model 228. For example, the lOOV, 1A range is increased to lOOV, 3A output. 26 I I 228 82 O+ r-s+w- L Figure 15

48、. Configuring Two Model 228s for Higher Current Figure 16. Configuring Three or More Model 228s for Higher Current 27 Service Form Model No. Serial No. Date Name and Telephone No. Company List all control settings, describe problem and check boxes that apply to problem. Cl Intermittent 0 Analog outp

49、ut follows display 0 Particular range or functwn bad; spcclf) u IEEE failure 0 Obvious problem on power-up 0 Batteries and fuses are OK i-l Front panel operational 0 All ranges or functions are bad 0 Checked all cables Display or output (check one) 0 Drifts 0 Unable to zero 0 Unstable 0 Will not read applied input 0 Overload D Calibration only 0 Data required 0 Certificate of calibration required (attach any additional sheets as necessary) Show a block diagram of your measurement system including a