6ES7291-8GF23-0XA0 可亿可求
智能化数字电源系统的优化设计
介绍了数字电源系统的主要特点及发展现状，简要分析了组成系统的各类芯片的性能特点及工作原理，重点阐述数字电源系统的电路设计。为实现数字电源系统的优化设计提供了具体方案。
引言
开关电源正朝着智能化、数字化的方向发展。刚问世的智能数字电源系统以其优良的特性和完备的监控功能，正引起人们的关注。数字电源提供了智能化的适应性与灵活性，具备直接监控、处理并适应系统条件的能力，能满足任何复杂的电源要求。此外，数字电源还可通过远程诊断来确保系统长期工作的可靠性，包括故障管理、过电流保护以及避免停机等。
特点
数字电源系统的主要特点
数字电源系统具有以下特点。
1)它是以数字信号处理器(DSP)或微控制器(MCU)为核心，将数字电源驱动器及PWM控制器作为控制对象而构成的智能化开关电源系统。传统的由微控制器(μP或μC)控制的开关电源，一般只是控制电源的启动和关断，并非真正意义的数字电源。
2)采用“整合数字电源”(Fusion Digital Power)技术，实现了开关电源中模拟组件与数字组件的优化组合。例如，功率级所用的模拟组件——MOSFET驱动器，可以很方便地与数字电源控制器相连并实现各种保护及偏置电源管理，而PWM控制器也属于数控模拟芯片。
3)高集成度，实现了电源系统单片集成化(Power system on chip)，将大量的分立式元器件整合到一个芯片或一组芯片中。
4)能充分发挥数字信号处理器及微控制器的优势，使所设计的数字电源达到高技术指标。例如，其脉宽调制(PWM)分辨力可达150ps(10-12s)的水平，这是传统开关电源所望尘莫及的。数字电源还能实现多相位控制、非线性控制、负载均流以及故障预测等功能，为研制绿色节能型开关电源提供了便利条件。
5)便于构成分布式数字电源系统。
1pcs Yokogawa PLC F3YD64-1P
1pcs Yokogawa PLC MCM
1pcs Yokogawa PLC module F3PU01
1PCS Yokogawa PU01-0N
1PCS Yokogawa PU06-0N
1PCS YOKOGAWA SC-H6A6P tested
1pcs Yokogawa WT200
2 GE YOKOGAWA 50-152151FAFAETC1/M2143B-C PANEL METER 50152151FAFAETC1
2 GRAPHICS ConTROLS 30002508 2 FANFOLDED PACKS TO FIT YOKOGAWA B9573AN
2 Yokogawa Panel Meters analog YE-250-4 Range 0-1 mADC Scale 0-3000 & 0-1000
2 Rolls Graphic Controls Yokogawa B9708AR Roll Plot Chart Paper - 2 Rolls
2 YOKOGAWA AB40 AC AMMETER T8970
2 YOKOGAWA DB40 DC AMMETER T8968
2 Yokogawa Y870-00-0-FR Freq Panel Meter
2.5” Yokogawa 0-10 DC Amperes Panel Meter
2220 YOKOGAWA SERTEC 93D108 IM-H8A25ST163 INDUCTION MOTOR
2435:Chart Recorder
246955-580-AFA-0-0/JBB TRANSDUCER 3 ELEMENT 5A INPUT 60HZ 0-1MA OUTPUT
24931-380-AHD-1 24931380AHD1SA YOKOGAWA JUXTA 60Hz 120VAC CURRENT TRANSDUCER--SA
250 YOKOGAWA COUNTERS
250 YOKOGAWA COUNTERS REMANUFACTURED
250-340-LSRL Yokogawa A-C 0-200 Amperes Panel Board Ammeter
250429ECZZ8 - YOKOGAWA - 0-150 PANEL METER 0-50MVDC
250439LSZZ YOKOGAWA Meter 0-100AC Amperes Type 250 -
250440LSSN7JBM/UL Yokogawa Panel Meter 800A AC
250444PZPZ Yokogawa Panel Meter 0-150VAC NIB
250444RSSJ7JFJ/UL Yokogawa Panel Meter 0-600VAC
251244RXRX7JBU YOKOGAWA METER 2 1/2 INCH HLPM 0-300V 3A MML1339
251300DRDR8JLA YOKOGAWA INSTRUMENTATION
254329ECZZ - YOKOGAWA - PANEL METER 25-0 25 DC AMMETER
254429ECZZ - YOKOGAWA - 0-75 SCALE PANEL METER 0-1000DCMV
255309FAZZ - YOKOGAWA - 0-1 RANGE DC PANEL METER
255324ECSC8 DC AMPERES 0-400 DC MV 0-LEFT RIG-50MV
2601001-JLJ9 YOKOGAWA INSTRUMENTATION
261400FAFA9JBC ; Yokogawa ; Panel Meter 20 - 280KW
2901 YOKOGAWA 370 164 LR8100 Recorder
2901 YOKOGAWA RECORDER 370 164
2pc Yokogawa EXA PH monitors PH400-P-U-1-E 120v
3 Cases of 10 Boxes NIB YOKOGAWA B956DNC FOLDING CHARTS
3 ea. Yokogawa Pen Cartridge B9588kH Green
3 MISC PANEL METERS 251424ECSF 251410FAFA 250410FAFA FREE SHIPPING!
3 Pack B9902AP YOKOGAWA Chart Recorder Pens BLUE 3PC 3 PACK Cartridge
3 Yokogawa DP HARP EJA-430A TRANSMITTERS
3 Yokogawa Pen Chart Recorder DC Amp Plugins(L) for Type 3056 R o C
3 Yokogawa Violet Fibre Chart Recorder Pens Graphic Controls 30960689 NOS
3" S/S Ball Valve w/Yokogawa EJA210A Press Transmitter
30 NOS Yokogawa blank panel meters YEW 286111FAFA NTK0843 04 41- 858
34906 In box, Yokogawa 250-3 Panel Meter 0-600VAC
3-Yokogawa, type 260, 15-0-15 dcv, NOS, free shipping, 30 day warranty
4 YOKOGAWA STRIP CHART RECORDERS R10000 model 436002
400 AMP PANEL METER AC AMPERES YOKOGAWA 250440LSSC Rating 0-5A
4266 uR100T Yokogawa µR100T Industrial Recorders 4266 suffix -82-11/SC12
56K8303 Yokogawa 250-340-Nlnl Current Meter
5pcs Yokogawa FA-M3 F3RS41-0N F3RS410N PLC Comm Module 3 Months Warranty
6306 YOKOGAWA SC402 SC402G-E-1-E ConDUCTIVITY TRANSMITTER 115V
64K0359 Yokogawa 254250Anan Frequency Meter
73K5726 Yokogawa B9565Aw Chart Paper
81C7474 Yokogawa 254-350-Anan Frequency Meter
8637 YOKOGAWA DL3110B DIGITAL OSCILLOSCOPE 700310 -1/D/PRN/EXTMEM
9 SEALED Boxes Yokogawa Fanfold Strip Chart B9627AY 30695418 RECORDING CHART
A pairs Yokogawa 700952 150 MHz Passive Probe
a set of YOKOGAWA DD vigorously from the direct-drive motor DM1045B00+SD1045B02
AAI135-H00 S2 Yokogawa AAI135 Analot input module **Free Express Shipping
AAI835-H00 S2 Yokogawa AAI835 Analog I/O Module ATK4A00 S1 Block **Free Express
A-B Allen Bradley Yokogawa 250320NTNT 0-50 DCV 250-320-NTNT Panel Meter VDC Volt
ACM11-S2 Yokogawa AcM11 S2 Revison U1 H4 F6 Communicaiton Module
ADMAG AE YOKOGAWA AE102MG AB1-LSA-A1DH MAGNETIC FLOWMETER SIZE 2.5
ADMAG AE YOKOGAWA AE115MG AB1-LSA-A1DH MAGNETIC FLOWMETER TEFLON PFA
ADMAG AE YOKOGAWA AE202MG CB1-ESA-A1DH MAGNETIC FLOWMETER SIZE 25 mm
ADMAG YOKOGAWA MAGNETIC FLOWMETER AE205MG, AE205MG-AB1-LSA-A1DH/BR, 2"
ADVICE Yokogawa digital Computer AD200B-S50C with PP150 SM850X Probe PU550B
AGILENT HP 4261A LCR Meter Yokogawa
Agilent(Keysight) DSOX3102A Oscilloscope; 2Ch 1GHz
AMN11 YOKOGAWA DCS 60 days warranty
AMN33-S2 Yokogawa AMN33 S2 Nest for Communication Modules
Amp Meter 20-40A Yokogawa
Ando / Yokogawa AQ2202 Main frame Controller
Ando / Yokogawa AQ2735 Sensor Unit W/ AQ9389B Input Adapter for Use With AQ2140
ANDO AE5135 Protocol Analyzer / yokogawa
ANDO VN7100 WIDEBAND MODULATION ANALYZER YOKOGAWA
Ando Yokogawa AQ2200-331 ATTN Module, 62.5GI
Ando Yokogawa AQ2200-411 OSW Module, 62.5GI, A-4
Ando Yokogawa AQ2200-411 OSW Module, 62.5GI, A-8
Ando Yokogawa AQ2200-421 OSW Module, 62.5GI
Ando Yokogawa AQ2200-421 OSW Module, 62.5GI A-1,2
Ando Yokogawa AQ2200-421 OSW Module, Single Mode
Ando Yokogawa AQ2200-421 OSW Module, Single Mode, A-1,2
Ando Yokogawa AQ2202 Main frame Controller, TESTED, EXCELLENT CONDITION
Ando Yokogawa AQ8201A AQ8201-33M AQ8201-33 AQ8201-110 AQ8201-412 AQ8201-422 Mods
Ando Yokogawa AQ8202-322 ATTN Module, 62.5GI
Ando Yokogawa AQ8202-412 Dual 1x2 OSW Module, 62.5GI
Ando Yokogawa AQ8202-414 OSW Module 1x4, 62.5GI
Ando Yokogawa AQ8202-418 OSW Module 1x8, 62.5GI
Ando/Yokogawa AQ4321A Tunable Laser Source
Ando/Yokogawa AQ4321A Tunable Laser Source, 1480-1580nm
Ando/Yokogawa AQ8201A Fiber Test Mainframe w ITU & Tunable Lasers, Detector, MUX
ANDO/Yokogawa OTDR AQ7275 SM OTDR with AQ735032 Module,1310/1550 38/36 dB
APC YOKOGAWA SU039 * IN BOX* 3 Available
AS S9361 DH-00 Terminal Block for Digital I/O Module SDV541-S33 S1 Yokogawa **Fr
B9946TT Sub -CPU Board Assy for Yokogawa DL708E 8 Channel scope
Battery Contacts Corrosion YOKOGAWA 2426A DIGITAL INSULATION TESTER Repair Parts
BRAND IN BOX YOKOGAWA STRIP CHART RECORDER R10000 model 436102
Brand No. 55T8782 Yokogawa Ut35A - 000 - 11 - 00 Controller Temperature
Brand No. 73K5758 Yokogawa 240001Aaaa Digital Time Meter
BRAND ROTA YOKOGAWA D-79664 WEHR 2012 95 PSI G 300 CFM ATEX AND/OR PED
BRAND YOKOGAWA DCS AAM10 Analog Input Module PLC
Brand Yokogawa/Ando AQ1200A OTDR /w SM module 1310/1550 34/32 dB
Cable for GE / Yokogawa
Circuit board C4555-60004 power supply yokogawa PS040A-0102 B-6
Cole Parmer Yokogawa 60 AC Ampere Scale EW-18001-97 NIB
COMPUMOTOR DYNASERV SR1060B62
COMPUMOTOR YOKOGAWA DR-5070B-230 SERVO DRIVE
Controller for blue M 19831 yokogawa
CP451-10 S2 Yokogawa Processor Module CP451 Suffix 10 Style S2 **Free Shipping
CP451-11 S2 Yokogawa Processor Module CP451 Suffix 11 Stype S2 *Free Shipping
CPU F3SP25 Yokogawa 60 days warranty
CR5 PA*A YOKOGAWA DCS QTY
Crompton 077427AQQA*** Power Meter, GE Catalog 103402FCAD7 Type AB40
DB40 RR404 Yokogawa Panel Meter 0-500 KW Rated 4/20 mADC
DC KILOAMPERES, YE/251324ECVA,R: 0-50 MVDC,S:0-1.0,C:DC KILOAMPERES
DCS AD5*D YOKOGAWA 60 days warranty
DCS YOKOGAWA ADM12C 60 days warranty
DD servo Actuator
Demodulator M602B yokogawa Denshikiki
DL1540 Digital Oscilloscope 8bits 200MS/s 150 MHz Model 701510 | Yokogawa
DM1100A00 200MM28694J0 YOKOGAWA DD SERVO ACTUATOR 94S1698 MOT-I-87
DP HARP EJA-430A TRANSMITTER * OLD STOCK 430 PSI YOKOGAWA GAUGE PRESSURE
DPharp EJA EJA430A-EAS4A-97NA/K1 YOKOGAWA
DPharp EJA EJA430A-EAS4A-97NA/K1 YOKOGAWA
DPharp EJA EJA430A-EAS4A-97NA/K1 YOKOGAWA #ZL02
DPharp EJA EJA430A-EAS4A-97NA/K1 YOKOGAWA VCAU
DPHARP TRANSMITTER EJA 110A0LS4B-92EA/FF1/01 EJA 110A 0LS4B-92EA/FF1/01+ M4AVIC
DX1002-1-4-1 YOKOGAWA DX1002-1-4-1 DAQSTATION Digital Recorder Options
DYNASERV DD SERVO ACTUATOR SD1075B02-2SO YOKOGAWA USE MOTOR 199MM21669M9
DYNASERV DD SERVO ACTUATOR SD1100A02 for 200MM28694J0 YOKOGAWA AC MOTOR
DYNASERV G3 SERVO DRIVE ACTUATOR ,UR1BG3 YOKOGAWA
DYNASERV SERVO ACTUATOR :SD1015B02 YOKOGAWA
DYNASERV SR1015B02-2SN DD SERVO ACTUATOR YOKOGAWA SERVO DRIVE
DYNASERV SR1045B02-2SN DD SERVO ACTUATOR YOKOGAWA NIB
E7000GA AS E7000GK-01 E7000GL-01 PCB CIRCUIT BOARD D507671
ELECTRO-METERS 250-321-MTXS YOKOGAWA 200-0-200% LOAD 10V-DC PANEL METER B455524
ELECTRO-METERS 250-321-SMSM YOKOGAWA 0-750 DC VOLTS VOLTAGE PANEL METER B453605
ELECTRO-METERS YOKOGAWA 250-321-MTXS 200-0-200% PERCENT LOAD METER B453614
ELECTRO-METERS YOKOGAWA 250-321-MTXS SCALE 200-0-200 PERCENT PANEL METER B487654
EP3*A YOKOGAWA DCS 60 days warranty
F3LC51-2N Yokogawa 60 days warranty
F3NC12-0N Yokogawa styles S1 2 axis position module - - 1 Year warranty
F3RZ81-0N PLC Module YOKOGAWA F3RZ810N 1PC 1FFZ
F3RZ82-0F YOKOGAWA PLC module good in condition for industry use
F3RZ91 F3RZ91ON YOKOGAWA RS422 Interface Communication Module 19,200 BPS MAX 1
F3SP20-ON Yokogawa 60 days warranty
F3WD643P AUTOMATION SYSTEM PLC MODULE 1PC YOKOGAWA F3WD64-3P MVA5
F3YD14-5A Yokogawa 60 days warranty
F3YP14-0N Automation System 1PC YOKOGAWA PLC MODULE F3YP140N L9N5
Factory Ace Spo8-Op Yokogawa Programmer Power Supply Electric Box
Fairweather Instruments TPS66HTX-RS-RTP w/ Yokogawa UP350 Temperature Controller
Fisher Scientific Oven Model 825F w/Yokogawa UT150 Controller, 325C Max., #38470
FOR PARTS YOKOGAWA UR180-700-31 STRIP CHART RECORDER PLOTTER INV=15630
For Spare Parts No Working Yokogawa 520 02 Shadow Cylinder luminance Colorimeter
FOSTORIA / YOKOGAWA AC VOLT METER YE/260344SFSF
FU20-05-T1-FSM Yokogawa 4 in 1 pH Sensor
G118932 Yokogawa SD1004B64 Parker Compumotor Dynaserv DM-1004B-115 Servo Drive
G97586 Yokogawa MT6121 Wafer Memory Test System, Dual Head Configuration
GE / Yokogawa DB40 Ammeter - 0 To 2500 AMPS - 10311FAZZ
GE / Yokogawa DB40 Ammeter 103111FAZZ, Scaled 0 to 50 DC Amperes, -Old-Stock
GE / Yokogawa Panel Meter 0-10 DC Amperes 251200MTMT
GE 0-300 Type 180 Edgewise Instrument
GE General Electric 103021PZUL 0-5250 Volt AC Switchboard Meter Yokogawa
GE General Electric 103111FAFA7UTC Switchboard Meter 0-2000 Kw/Kvar Yokogawa
GE General Electric 250300KAKA Yokogawa Panel Meter 0-200 DC Milliamperes NIB
GE SUPPLY YOKOGAWA 0-1200 AC AMPERES AMP METER 103131LSSV
GE Yokogawa 0 - 150 vdc Analog Panel Meter model 255
GE Yokogawa 0 - 30 vdc Analog Panel Meter model 255
GE Yokogawa 250240LSSJ, 0-600 A-C Amperes Panel Meter
GE YOKOGAWA 250339FTZZ AC Panel Meter 0-600VAC (LOT OF 2)
GE YOKOGAWA 3.0W Elapsed Time/Hour Meter; Motor 120VAC; 60Hz; 2.5in;
GE Yokogawa 30 0 30 vdc Analog Panel Meter 50-2552221NLNL1 model 255
GE Yokogawa 4 1/2" Big Look 0-30A AC Amperes Gauge 250-440-NLNL
GE Yokogawa 50 0 50 dc microamps Analog Panel Meter 50-255201CYCY1 model 255
GE Yokogawa 50 0 50 dc milliamps Analog Panel Meter 50-255201HYHY1 model 255
GE Yokogawa 500 0 500 dc milliamps Analog Panel Meter 50-255201KMKM1 255
GE YoKogawa 50-2514095FAZZ1 Panel Meter 0-150 VDC
GE Yokogawa Admag AXF01 5H Magnetic Flow Meter
GE Yokogawa Analog RPM Panel Meter 0-2500rpm
GE Yokogawa Big Look 2.5" RPM Panel Meter 0-2500 YE/255300DRDRJBT NIB
GE YOKOGAWA DC Amperes Meter 250229ECZZ8 0-10
GE Yokogawa Medical Systems Ultrasound probe / Transducer
GE Yokogawa Model 25429 A-C Amperes Panel Meter
GE Yokogawa Panel Meter 0 - 10 MADC YE 250200 GZGZ
GE YoKogawa Panel Meter 0 - 10 VDC YE 254320 MTMT
GE YoKogawa Panel Meter 0 - 50 VDC YE 250320 NTNT
GE YoKogawa Panel Meter 500-0-500 UADC 250 4 N BOX
GE Yokogawa Panel Meter YCA 2504 400-0-400 DC Amperes 4-7/8" W X 4-3/8" L
GE YOKOGAWA PTMST PWA PN 5331669 / PN 51331666-4 / PN 5331669-2 + CPU MODULE
GE Yokogawa YE 25432MTMT 1 - 10 DC Amp Panel Meter
GE/ YOKOGAWA 2513 44MT MT * IN THE BOX*
GE/ YOKOGAWA 50.250340LSP21AAA * OUT OF THE BOX*
GE/YCA 250-340-LSVA YOKOGAWA AC 0-1kA PANEL BOARD METER
GE/YOKOGAWA 103131LSNG7 AMP METER 0-20A ***NNB***
General Electric / Yokogawa: Model: 251-3 AMP Meter 0-15A DC. Old Stock
General Electric Yokogawa 103 AB40 U
General Electric Yokogawa 250201HYHY 50-0-50 DC Milliamp Analog Panel Meter 2.5"
GOOD Yokogawa AB40 0-600v AC Voltmeter (KK1)
GOOD YOKOGAWA SERTEC GEAR BOX 7RH2-D5 7RH2D5 86MR
Graphic Controls Blue Yokogawa 64-42-0303-03 B9902AP
Graphic Controls Chart Recorder Plotter Pens (3) Yokogawa 82-24-0103 30944634
Graphic Controls Recording Charts 30695418 1P30695418 fits Yokogawa B9627AY
Graphic Controls Yokogawa Chart Paper, 12/LOT, P/N B956BEQ
Graphic Controls YOKOGAWA E9721PB/PF Red Fibre Chart Recorder Pen Lot of 3
Graphic Controls Yokogawa, B9565AW, B9565 AW,Folding Chart,Recording Paper,0-100
Graphics Controls 30002508 2 Fanfolded Packs to fit YOKOGAWA B9573AN *
GUARANTEED / LITTON YOKOGAWA FINESERV MKII PC/10020 POSITION ConTROLLER UNIT
H.P. (Yokogawa) / Agilent: Model: 16048A Test Leads B
H.P. (Yokogawa) / Agilent: Model: 16096A Test Fixture B
H10 PRO "TOP GUN" LEAK DETECTOR *1 SLOT CHARGER STAND
H-10 Professional All Refrigerant Leak Detector Yokogawa
High Precision YOKOGAWA AQ1200A SM OTDR 1310/1550nm, 30/28dB Fiber Optic OTDR
HOFFMAN Pump Control Box in A16148CHSCFG Enclosure / Yokogawa UT320 / RL PAXP
HP 4141B DC Source Monitor (Yokogawa Model No. 4062B Made in Japan)
HP 41421B Source/Monitor Unit,40uV-100V/201A-100mA,Yokogawa, ,Japan(3773)
HP AGILENT 4500 ICP-MS YOKOGAWA G1820A SHIELD TORCH
Hp Agilent Keysight Yokogawa 4194A Measurement Unit w/ Opt 350,001
HP Oscilloscope probes for YOKOGAWA Oscilloscope
HP Power Module DC Converter PS604-0101 Yokogawa 0950-2232
HP Yokogawa 0950-3017 PS605-0101 Power Supply
HP/YOKOGAWA 4261A LCR METER W/SERVICE/OPERATING MANUALS/SCHEMATIC
IPM Yokogawa Panel Meter Ye/250 3/0 10VDC MH1 4149k16g0813 Quantity 2
Iwaki EH-F70V6C10-20J Metering Pump (free shipping)
JISC1731 Yokogawa 2267 15VA NO FUSE 20:1 2200/110 Potential Transformer - EOK
JOHNSON ConTROLS / YOKOGAWA 602-000-046 ConTROL MODULE - w/GUARANTEE
Johnson Controls / Yokogawa T-5002 202 Transmitter
JOHNSON ConTROLS YOKOGAWA YEWFLO VORTEX FLOW ConVERTER YFA11 24 VDC 359ER03
Johnson Yokogawa 436001 Chart Recorder GOOD CONDITION
JOHNSON YOKOGAWA ADMAG MAGNETIC FLOW TRANSMITTER, AM 202DN, SIZE:25 MM 1",
Johnson Yokogawa B9565 Servo Amp Assembly B9565LH-10
Johnson Yokogawa Blackbox Switch A-E Model SW026A FFFFF(HK626)
Johnson Yokogawa DPharp EJA3104 Transmitter EJA-3104
Johnson Yokogawa DPharp EJA440A Transmitter EJA-440A
JOHNSON YOKOGAWA IAC5 Input Module Relay Lot of 5
JOHNSON YOKOGAWA OAC5 Lot of 2 Input Module Relay
Johnson Yokogawa Vortex Flow Converter / Transmitter YFA11
Johnson Yokogawa Vortex Flow Converter YFA11-AUPA-04*E 24 VDC 4-20mA
JOHNSON YOKOGAWA VORTEX FLOW ConVERTER YFA11-AUPA-08*E NIB
JOHNSON YOKOGAWA YA 43F-SBS4 TRANSMITTER 4-20 MA ( )
Johnson Yokogawa Yewflo YF101 Vortex Flow Meter Converter Transmitter Japan
JOHNSON YOKOGAWA YEWFLO YF105 VORTEX FLOWMETER ***XLNT***
JOHNSON YOKOGAWA YF102 YEWFLO VORTEX FLOWMETER, 24 VDC, 0-60 GPM,
JOHNSON YOKOGAWA YF102-ALSB1A-S3S3-C/FMF/SCT VORTEX FLOWMETER DC24V 4-20MADC
JOHNSON YOKOGAWA YF105-NNNB2A-S3S3*C/FMF VORTEX FLOWMETER CONDITION
JOHNSON YOKOGAWA YT200-D2NA/FMF/SCT * *
JUXTA / YOKOGAWA-Model #FM1V*A - DC Voltage Transmitter -