U n i n t e r r u p t i b l e P o w e r S y s t e m

Similar documents
USER MANUAL ONLINE UPS 6000L(XL)/10000L(XL) Uninterruptible Power Supply

On Line UPS. LUC 1000E / LUC 2000E / LUC 3000E User Manual

Uninterruptible Power System

Uninterruptible Power System

Aurora Single Phase Emergency Lighting Inverters

Uninterruptible Power System

USER S MANUAL CONTENTS. Uninterruptible Power Supply 1. INTRODUCTION SAFTY INSTRUCTION SYSTEM DESCRIPTION... 4

UniStar III Series. Full Three Year Warranty. On-line, Single-phase UPS System. 1, 2, & 3kVA Tower Model

DC AC POWER INVERTER. LIV 10 / LIV 20 / LIV 30 User Manual

NB NB 1511 NB NB 4031 TRUE ON-LINE DOUBLE CONVERSION UPS

gimagination at work Technical data sheet Uninterruptible Power Supply LP Series 6 & 10 kva GE Digital Energy

Uninterruptible Power System

3. MAJOR SYSTEM COMPONENTS Emergency Lighting Power System shall consist of the following major subsystems:

POWER TROLLEY 8 INSTRUCTION MANUAL POWER TROLLEY 8. Model: SINE Instruction Manual for: Self-Contained Sinewave Mobile Power Backup System

CONTENTS 1. INTRODUCTION SAFTY INSTRUCTION CABLE CONNECTION SYSTEM DESCRIPTION INVERTER OPERATION...

800VA/ 1000VA/ 1200VA/ 1500VA 2200VA/ 3000VA USER S MANUAL

User Manual 1KVA/ 2KVA/ 3KVA INVERTER / CHARGER

TECHNICAL DATA SHEET KVA UPS Systemss

SAVER DSP SERIES. 3-10kVA USER MANUAL

USER MANUAL. Power GUARD UPS. Uninterruptible Power System

EFFEKTA Power Supplies

User Manual SOLARMAX 1KVA/ 2KVA/ 3KVA INVERTER / CHARGER

User Manual 4KVA/ 5KVA INVERTER / CHARGER. With MPPT Controller

Model ESV Uninterruptible Power System 1.5 KVA/KW KVA/KW Single Phase

APC Smart-UPS. GUIDE SPECIFICATIONS FOR 1000VA & 2000VA Smart-UPS 230VAC Uninterruptible Power Supply

User Manual 1KVA-5KVA INVERTER / CHARGER

Technical data sheets

Informer Compact Series

TOWER MAXI T SINGLE CONVERSION ON LINE UPS SYSTEMS

User Manual V1.1 OptiFlex 1100 / OptiFlex 2000

OutdoorXUPS-600AHV-8364

User manual. Solar Hybrid 1-5KVA. Uninterruptible Power Supply / Charger

POWER kva Nominal output power (Cos φ0,8) kva Nominal output power (Cos φ1,0) kw >88 Efficiency (AC AC)

CONTENTS 1. INTRODUCTION SAFTY INSTRUCTION CABLE CONNECTION SYSTEM DESCRIPTION OPERATION... 9

POWER kva

Back-UPS 650 VA 230 V with AVR (BX650CI-ZA)

POWER kva

MKN-DSP SERIES - THREE PHASE

User Manual 1.5KVA-3KVA INVERTER / CHARGER

User Manual 1.5KVA-3KVA INVERTER / CHARGER. Version: 1.1

Foreword. Manual instruction

CENTAURI ENERGY SERVER TECHNICAL DATA kw POWER

Solar Hybrid Power Generating System CPS1200EOH12SC CPS2200EOH24SC CPS3000EOH24SC. User s Manual K01-C

LINE INTERACTIVE LONG BACKUP TIME UPS EN-1000 / EN-2000 USER S MANUAL

Illuminator Series CR NEMA 3R

TECHNICAL SPECIFICATIONS OF 2 KVA POWER CONDITIONING UNIT

.3 Section Waste Management and Disposal.

Solar Hybrid Inverter SP Efecto Series

Users Manual. Defender 1 8.0KW to 14.0KW Online Emergency Lighting Inverter. Technical Manual # Revision B

Illuminator Series CM. GUIDE SPECIFICATIONS And TECHNICAL DESCRIPTION. 500W, 1000W, 1500W and 2000W Single-Phase Emergency Power System

User Manual 1KVA-5KVA INVERTER / CHARGER

1. INTRODUCTION SYSTEM DESCRIPTION Front Panel CONNECTION AND OPERATION TROUBLESHOOTING...8

Whad 0.8, 1, 1.5 kva. Manuel d installation Installation manual. Part. LE05733AA-07/12-01 GF

User Manual Back-UPS BX650CI-MS 230 Vac with AVR

POWERTRONIX QUASAR 5-40 KVA

Fortress 1 Outdoor Emergency Central Lighting Inverter (CLI) Technical Specifications

TECHNICAL SPECIFICATION FOR A 10 TO 50 KVA THREE PHASE, UNINTERRUPTIBLE POWER SYSTEM WaveRider III

BRAVER UPS. (Uninterruptible Power System) User s Manual

Power Inverter. User s Manual. Diamond Series CPD1200EILCD

Technical Data Sheets

Power Lynx 3 Uninterruptible Power System (UPS) Technical Specifications

Cobra 3 Stand-By Emergency Central Lighting Inverter (CLI) Technical Specifications

HYBRID 5048E. Hybrid Inverter INSTALLATION AND OPERATION MANUAL. Version 2.0E

General Precautions. Personnel Precautions

User Manual 5KVA/5KW INVERTER / CHARGER. Version: 1.3

Technical data sheet VH UL. Digital Energy Uninterruptible Power Supply. GE Digital Energy Power Quality

Users Manual. Cobra Plus Stand-By Emergency Lighting Inverter. Technical Manual # Revision B

On-line, Single Phase, Double Conversion UPS

TECHNICAL DATA SHEET INFINITY kva 3Ph(in) 3Ph(out)

SmartOnline SUT Series 3-Phase 208/120V 220/127V 20kVA 20kW On-Line Double- Conversion UPS, Tower, Extended Run, SNMP Option

SmartOnline SUT Series 3-Phase 208/120V 220/127V 30kVA 30kW On-Line Double- Conversion UPS, Tower, Extended Run, SNMP Option

MPPT Controller PVTS Series User Manual. User Manual. 800W-4000W Hybrid solar inverter. Version: 1.4

User Manual 3KW/5KW INVERTER / CHARGER. Version: 1.0

User Manual. Axpert King 3.2KW/5.2KW 48V MPPT SOLAR INVERTER. Version: 1.0

Solar Hybrid Inverter SP Brilliant Series

Series 120/120VAC Universal Tower/Rack Mount

UPS Wizard User s Manual

1KVA/ 2KVA/ 3KVA/ 4KVA/ 5KVA MS, LV MPPT INVERTER / CHARGER. User Manual. Version: 2.3

U P S. Uninterruptible Power System Unterbrechungsfreie Stromversorgung

UPS USER MANUAL F-11 LINE INTERACTIVE UPS GENERAL PURPOSE UPS 650VA/1200VA/2200VA

User Manual 1KVA-5KVA INVERTER / CHARGER. Version: 2.1

ConceptpowerTM Modular kVA

SmartOnline 120V 2.2kVA 1.8kW Double-Conversion UPS, 2U, Extended Run, Network Card Slot, LCD, USB, DB9

Technical Data Sheets

Uninterruptible Power System. Line Interactive Network Protection Pure Sine Wave Output UPS. Rack Mount Models 1000VA/ 1500VA/ 2000VA/ 3000VA

Solar Hybrid Inverter SP Efecto Series

USER S MANUAL ENDURE 500VA ENDURE 750VA ENDURE 1000VA ENDURE 2000VA

Smart-UPS VT APC Smart-UPS VT 30kVA 208V w/4 Batt. Modules, Start-Up 5X8, Internal Maintenance Bypass

Eclipse Plus VA UPS and Surge Suppressor User s Manual

Sola/Hevi-Duty S3K Series Mini-Tower UPS

Defender Mini Online Emergency Central Lighting Inverter (CLI) Technical Specifications

The power behind competitiveness. Delta UPS - Amplon Family. N Series, Single Phase 6/12 kva. User Manual.

Standard 1000VA, 2000VA & 3000VA Universal Tower/Rack Mount LB Extended Models 900VA, 1700VA & 2500VA

Uninterruptible Power Supply

POWER+ PREMIUM CBS. BS-EN Emergency electrical installations Electric power systems Emergency lighting Escape lighting

Fortress 3 Harsh. Harsh Environment. Emergency Central Lighting Inverter (CLI) Technical Specifications

Technical Data Sheets

Tower Electronic Systems

User Manual. 1P-1P 6KL/7.5KL/10KL Online UPS

Transcription:

SMART ON-LINE UPS User s Manual U n i n t e r r u p t i b l e P o w e r S y s t e m Smart On-Line UPS 2KVA ~ 20KVA

20KVA Exhaust hole (16)Main breaker (12)Heat exhaust hole (15)Telephone (Rj11) or network (Rj45) port (13)Communication port (18)External battery outlet (22)Output breaker (20)Bypass breaker (17)Power I/O terminal block 4-1 Function Description (1) LCD display panel Displays the UPS status (2) Select/Light key Allows you to select the LCD screen display on panel, and illuminates when the background light is suspended. (3) Over charge LED LED is on when the battery charging voltage is too high. (4) BAT. level LED Indicates the battery capacity level (5LED s). LED flashes and decreases when the external power is suspended. (5) Over load LED LED flashes when UPS output is overloaded. (6) Fault LED LED is on when UPS is abnormal. (7) Bypass LED LED is on when UPS power output supplied from by-pass. (8) Inv. LED LED is on when the status of the inverter is normal. (9) Line LED LED is on when the line input is normal. (10) Inv. ON/OFF switch This switch allows you to turn on and off the UPS. (11) Battery discharging LED LED flashes when the utility power is failured otherwise this LED is off. (12) Heat exhaust hole This hole allows the system to release the internal heat of the UPS. (13) Communication port This connector allows the UPS to connect the computer. (14) Output receptacles This is the output receptacles of the UPS. Electrical apparatus with relatively smaller load can be connected to this outlet. (15) Telephone(RJ11) or network(rj45) port Modem and fax machines and computers are protected by integrated surge absorbing element. (16) Main breaker This breaker controls all the power of the UPS. - 11 - - 12 -

(17) Power I/O terminal block UPS utility power input, the external battery and the output power are connected to this port. (18) External battery outlet This outlet is used when battery is connected outward. (19) Battery breaker This is the power breaker of the battery. (20) Bypass breaker This is a bypass used when fault occurs in the UPS. (It remains OFF normally.) (21) Input breaker This is the breaker of the UPS utility power input. (22) Output breaker This is the breaker of the UPS AC power output. (It remains ON normally.) 5. Connection/Installation 5-1 Input 1. First of all, make sure the UPS specification is in conformity with the input. Please do not connect to a household wall outlet if the current is higher than 15 A. 2. Take off the cover when connecting the lines, put the cover back when finished. 3. Please refer to the following drawings for wiring, and do not connect the electrode to the opposite positions. 4. In shortage of neutral wire from the AC input power source, connect the wire with higher voltage to the front line position and the wire with lower voltage to the neutral position. 5. Make sure the grounding procedure is completed for the safety operation of the computer and personnel. 6. Turn off the power when connecting. (Caution When constructing, please abide related regulation for electrical work.) 7. Do not use additional apparatus on the same switch when connecting to the power distribution panel. 8. The L on the terminal block stands for the front line position, N for the neutral wire position, G for the grounding position, B+ for the position pole of the external battery and B - for the negative pole of the external battery. 10K 15KVA Exhaust hole (21)Input breaker (20)Bypass breaker (12)Heat exhaust hole (15)Telephone (Rj11) or network (Rj45) port (13)Communication port (18)External battery outlet (19)Battery breaker (22)Output breaker (17)Power I/O terminal block - 13 - - 10 -

2K 10KVA I/P 1 2W O/P 1 2W (12)Heat exhaust hole I/P 1 2W O/P 1 3W (15)Telephone (RJ11) or network (Rj45) port (13)Communication port (16)Main breaker (14)Output receptacles (17)Power I/O terminal block I/P 3 O/P 1 2W - 9 - - 14 -

5-2 Output 1. Some UPS models have outlets on their back. Any apparatus with lower load of 15 A can be connected, and for the higher than 15 A or long distance, connection to the output terminal block is necessary. 4. The exterior structure and functions 2. Please refer to the following drawings when connecting, and do not reverse the electrode directions. 3. Please refer to INPUT section for the Work specification. 4. Please avoid short and overloading. I/P 1 2W O/P 1 2W I/P 1 2W O/P 1 3W (1) Lcd panel (2) Select/Light key (7) Bypass LED (3) Over charge LED (8) Inv. LED (4) BAT. Level LED (9) Line LED (11) Battery Discharging LED (5) Over load LED (10) Inv. ON/OFF switch (6) Fault LED Lcd display panel - 15 - - 8 -

3. Technical Specifications 6. Operation Model Input Output Capacity 202 302 402 502 602 802 103 123 153 203 2KVA 1.4KW 3KVA 2.1KW 4KVA 2.8KW 5KVA 3.5KW Voltage 115V, 230V +/-25% 6KVA 4.2KW 8KVA 5.6KW Frequency 50Hz or 60Hz ±5% Phase Voltage THD Voltage Regulation Frequency Stability Crest Factor Transient Response Short Circuit Wave Form 1 2? G 10KVA 7KW 12KVA 8.4KW 15KVA 10.5 KW 190V, 208V, 220V, 230V, 240V, 380V 20KVA 14KW 1 2? G or 3 3? G or 3 4? G 100VAC, 110VAC, 120VAC, 220VAC, 230VAC or 240VAC ± 1% 3% (Linear Load) ± 0.5% (Free running) 3 1 ± 5% (100% load change) Auto cut-off output no transferring to bypass Sine-Wave ± 1% (±3% with ISO Transformer) 6-1 Turn on the UPS for the very first time 1. Sway the input/output cable by hand and check if it is loosen, if so, tighten it again. 2. Check input voltage, and see if it conforms to the specification of the UPS. 3. Pull every circuit breaker 16 upward on the back of the UPS. (Some breakers over 10 KVA are sealed by cover, please do not remove for maintenance purpose.) At this moment, LINE LED (9) and BYPASS LED (7) are on, UPS output is exactly the same as the utility power. 4. Push the INV ON/OFF switch (10) and UPS executes auto self-monitoring. At this moment INV LED (8), LCD Display panel (1) and BAT. LEVAL LED (4) are on, and after about 20 seconds the BYPASS LED (7) is off, which indicating the normal operation of the UPS. 5. Measuring the output voltages, and see if it fits your requirement. 6. If everything goes on smoothly, please turn on your electrical apparatus to enjoy safety use. Battery Indicator Audible Alarm Environment Appearance Transfer Time Overload Capacity Efficiency Battery Voltage Battery Type Back up Time (Full) Zero-cross transfer 105%~150% for 30 seconds > 150% for 10 cycle 83% Lead acid maintenance-free battery 192V 14mins 8mins 6mins 8mins 6mins 5mins 3mins 4mins 9mins 5mins Recharge Time 5 hours to 90% 8 hours to 90% LCD LED Utility Power Fail Low Battery Fault, Over Charge Overload Humidity Temperature System operating status display, input / output voltage, frequency, output loading%, battery voltage, temperatures Line (green), inverter (green), Bypass (orange), battery (green), fault (red), overload (orange), over charge (orange), battery level (5 LED indicators) Beeping every 4 seconds approx, 2min. Auto-alarm reset Rapid beeping every second as battery approached final discharge Continuous Beeping 2 seconds on every other second 0~90% (non-condensing) 0 ~40 (32 ~104 ) Audible Noise < 50db < 60db Weight (kgs) 75 80 88 120 130 140 156 234 Size W*D*H 235*585*620 mm 265*634*735 mm 285*670 *895 mm Interface Communication RS232 / Dry Contact or AS 400 (Option) 320/41 0 336/43 6 353*930*1017 mm 6-2 Turn the UPS off Turn off all equipments connected to UPS. Push the INV ON/OFF switch (10) once again. After BYPASS LED (7) is on, but INV LED (8) off, LCD Display panel (1) and BAT. LEVEL LED (4) are off. Pull all circuit breaker downward on the back of the UPS. The turn off procedure is complete. 6-3 Turn the UPS on for daily use Just push INV ON/OFF switch (10) for daily use, no need to turn off the circuit breaker 16 on the back of UPS, otherwise recharging is failed. Note Auto system ON/OFF function is available when monitoring software is used. - 7 - - 16 -

6-4 Maintenance Switch Operate Procedure for 12KVA, 15KVA, 20KVA When UPS fails, users only have to turn off INV Switch (10). The maintenance procedure has to be operated by a technician, or any incorrect operating may damage the connected device (such as a computer) or even UPS. 2-2 On-Line UPS s Structure In Block Diagram The operate procedure is as following: 1. First, make sure INV Switch (10) on the front panel has been turned off. When INV Switch (10) is off, the power provision will be switched from INV mode to bypass mode automatically. 2. Remove the maintenance panel on the rear. Then, turn on Bypass Breaker (20). 3. Turn off Output Breaker (22). When Output Breaker is off, the power for any connected equipment (such a computer) will directly be provided by bypass. Attention!! Any incorrect procedure may cause power loss. 4. Now, maintenance of UPS can be preceded. (The mode of Input Breaker (21) or Battery Breaker (19) will not affect the power provision.) After UPS is repaired, the reboot procedure is as following: Make sure INV Switch (10) is in OFF mode -> Turn on the Input Breaker (21) -> Turn on Battery Breaker (19) -> Turn on Output Breaker (22) -> Turn off Bypass Breaker (Now UPS is ready for use.) 20 seconds after INV Switch is turned on, the power provision will be switched from bypass mode to INV mode. If everything works as usual, close the maintenance panel. The Smart ON-LINE UPS is a highly acclaimed reliable and intelligent designed UPS. The main features are such as: (1) RECTIFIER A Full-Bridge type rectifier to perform the filtering. (2) CHARGER For 3 8 K, the Charger Board is of Boost - Type. For 10 20 K the Charger Board is of Flyback-Type. (3) BATTERY BANK The whole ON-LINE UPS series is of 192 DCV, the battery capacity will be pertinently matched to the various models accordingly. (4) INVERTER The device of Inverter is of PWM 20KHZ Full-Bridge design with an Ultra Super Isolated Transformer added. (5) STS(Static Transfer Switch) It is functioned by both Relay and TRIAC together. To provide users the most considerate and convenience, there is a double display system design respectively LCD and LED to indicate a very comprehensive UPS operation mode status in case users are not available with soft ware application. - 17 - - 6 -

Whenever the Inverter occurs an unexpected fails or having too much load, circumstances like this for a well-designed UPS, it must be capable to detect by its Auto-detect circuit device and instantly transfer to By-pass (AC Line) by Static Transfer Switch without any interruption, the operation mode is printed in Bold-face line as Figure 1-2 (c). The Inverter will get back in operation when its fault is precluded, until then, the Load side will be supplied by By-pass or to be shut down if AC Line fails at this very same time. 6-5 The Operation and contents of the LCD display panel 1. Push INV ON/OFF switch (10) and the following screen will show up. WELCOME I/P VOLT XXX.XV The screen switches to the following after 4 seconds. ON BYPASS I/P VOLT XXX.XV Another 20 seconds later, UPS starts normally and screen turns to Figure 1-2(b) ON INVERTER I/P VOLT XXX.XV Pushes INV ON/OFF switch (10) once again to turn off the UPS and LCD display screen disappears. Figure 1-2(c) - 5 - - 18 -

2. The SELECT/LIGHT key (2) use The background light of the LCD display panel will auto-disappear after 3 minutes, pushes the SELECT/LIGHT key(2) again to have LCD background light again. There are two lines of words indicated on LCD display panel. Upper line indicates the UPS status and the lower line indicates various figures of UPS condition for user under following sequence I/P VOLT XXX.XV ( UPS input voltage ) O/P VOLT XXX.XV ( UPS output voltage ) BAT VOLT XXX V ( Battery voltage ) LOADING XXX % ( Load % ) FREQ XX.XHZ ( Input frequency ) TEMP XX.XC ( UPS Internal temperature ) More specifically, there are three respective drawings shown in the below can very clearly indicate how is the ON-LINE UPS really in operation modes. In Figure 1-2(a), the AC Line regularly supplies power to Converter, and then becomes Converter to supply power to Inverter, in the last is the Inverter supplies the power to the Load side. In the meantime, the charger is doing the charging into the Battery set. At the output sector, there is a Static Transfer Switch design to connect the Inverter with the Load, the Bold-faced line print in Figure 1-2(a) exactly shows this mode in operation. Push SELECT/LIGHT key once, you can change the screen data displayed on the LCD. 3. The meaning represented UPS status (LCD first line) ON BYPASS The UPS is under Bypass status. ON INVERTER The UPS works properly. BACKUP MODE The UPS is under utility power failure condition. LOW BATTERY Indicates the low capacity of battery. FAULT Some fault occurs on the UPS. UPS SHUTDOWN The UPS is off. UPS TESTING The UPS is executing the self-monitoring function. 4. Associated with monitoring software, additional functions are possible except the mentioned function by LCD. Figure 1-2 (a) In Figure 1-2 (b), please refer to the Bold-faced line print, when AC Line fails, the Battery set will instantly back up the power to the Inverter and uninterruptedly output to the Load side, the Load side actually will not be affected by the AC fails due to the Zero transfer time. The Battery set which supplies the power to Inverter will steadily keep its output to the Load side and will not be affected by the Battery set s voltage level, only the back-up time will be descended in accords with the decrease of the discharging current. The back-up time is subject to Ampere Hour (AH) or Battery capacity. - 19 - - 4 -

2. System Concept 2-1 On-Line Main Designs There are mainly three major parts to perform the ON-LINE UPS FUNCTIONS, they are AC TO DC Converter, Battery Bank as well as DC to AC Inverter which are all shown as the drawing in the below: 7. The communications interface of computer The computer communicational interface of UPS "Smart" series is True RS232 if integrated with LCD display panel, otherwise it is a simulative relay interface (DRY CONTACT) 7-1 Simulative relay interface(dry CONTACT) PIN FUNCTION 2 A closed circuit signal, which can be simulated by UPS when utility power is suspended. It remains open under normal condition and close when the utility power is suspended 4 The reference point of pin2 and pin5 5 A closed circuit signal, which can be simulated by UPS when battery capacity is low. It remains open under normal condition and close when the battery capacity is low 6 Remote control shutdown only 500ms of the voltage is required for this pin. This function is performed only under back up mode The figure above shows AC to DC Converter converts AC power into DC power and supplies power also to Inverter as well as to the Charger to proceed the charging to the batteries in the UPS. 7 The reference point of pin 6 Under normal operation status, the Converter supplies power to Inverter, whenever the AC Line fails, the Battery set will take the role to supply power to Inverter and output the requested Sine Wave to the Load side. - 3 - - 20 -

7-2 TRUE RS232 Interface 1-2 Cautions PIN FUNCTION I/O 6 RS232RX INPUT 7 GROUND INPUT 9 RS232TX OUTPUT 1. Read this user s manual thoroughly before your use. 2. Follow the indicated instructions step by step. 3. Please handle the machine with care when moving it. 4. When installing the power supply, be sure to follow the instructions. 5. Do not open the engine casting to avoid electric shock hazard to the personnel and machine damage. 6. Please recharge the battery for 12 hours every 3 months, when not in use for a long period. 7. Do not overload, it may cause UPS failure. 8. Always keep the UPS clean. 9. Please retain this user s manual within reachable range for future difference. Set up of the RS232 Interface is as following Baud Rate 2400bps Data length 8bit Stop bit 1bit Parity None - 21 - - 2 -

1. Introduction 1-1 The introduction of the system The "Smart" series UPS is a kind of smart on-line sine wave uninterruptible power system, which is intelligent, highly reliable and can provide good quality output AC power. The system is self-sustained and can display its input voltages, output voltages, frequencies, load, battery capacity, battery voltage, temperature and UPS status on both LED and LCD, and no need for the extra monitoring software. If monitoring software is put in use, the system can also achieve performances of self-examination, time switch and remote control through network, which allows users to manage the power more efficient from a distance. When external power is suspended or UPS battery low, the monitoring function can be triggered unmanned, to achieve the security function of turning off after auto saving system, so as to send out multilateral warning signals, including transmitting the warning message by e-mail automatically, calling the warning message automatically. The users no need to worry for the file the file loss by sudden power cut and real time contingency can be adapted when necessary. - 1 -

Contents *********** 1. Introduction. 1 2. System Concept.3 3. Technical Specifications..7 4. The exterior structure and its functions 8 5. Connection / Installation..... 13 6. Operation.. 16 7. The communications interface of computers. 20 8. Trouble shooting.....22