# How to resolve error about extra alignment tab?

\begin{table*}[!tp]
\tiny
\caption{Comprehensive analysis of the existing technologies, specifications, features and critical remarks} \label{table2}
\centering

\begin{tabular}{ p{1cm}| p{2cm}| p{2cm} |p{2cm} |p{1.5cm} |p{1.5cm}|p{1.5cm} |p{1.5cm} |p{3cm}}

\hline \textbf{Ref.} & \textbf{Line inspection} & \textbf{Fault detection} & \textbf{Fault classifications} & \textbf{OTLs deterioration problems} & \textbf{Fault localization} & \textbf{Fault diagnosis} & \textbf{Vegetation encroachment} & \textbf{Monitoring and control} & \textbf{Remarks} \\ [1ex]

\cite{IEEE2} & -- & \checkmark & \checkmark & \checkmark & -- &-- & -- & -- & The focus of the authors is on the methods used for fault detection, classification, and localization. However, fault diagnosis, monitoring, and controlling of OTLs are ignored.  \\ [1ex]
%  \hline

\cite{IEEE3}& \checkmark & -- & --  & -- & \checkmark &-- & -- & \checkmark & The aim of this article is threefold: a) review the deterioration problems accompanied with OTLs; 2) review existing OTLS inspection methods; 3) design condition monitoring system. However, ignored some crucial factors that significantly effect OTLs.  \\ [1ex]
%    \hline

\cite{IEEE4} & \checkmark & -- & -- & -- & \checkmark &-- & -- & \checkmark & Authors in this survey highlight gaps in the existing technology used for power lines inspection and provide guidance, how to move forward. However, fault diagnosis, vegetation encroachment, and control aspects of power lines are ignored   \\ [1ex]
%    \hline

\cite{IEEE5} & -- & \checkmark & \checkmark & \checkmark& \checkmark &-- & -- & The focus of the authors is on fault analysis and fault diagnosis based on intelligent systems. However, the causes of faults are ignored. & \\ [1ex]
%   \hline

\cite{IEEE6} &  & -- & \checkmark & \checkmark & \checkmark& \checkmark &-- & -- & The authors with support of ESKOM conducted a survey to highlight feasibility of WSN for monitoring and controlling OTLs. However, aspects accompanied with OTLs which compromise monitoring and controlling process are ignored.   \\ [1ex]
%   \hline

\cite{IEEE7}& -- & \checkmark  & \checkmark & \checkmark & \checkmark & -- & -- &-- & This paper is regarding the faults accompanied with power lines and solutions to overcome faulty situations. \\ [1ex]
%    \hline

\cite{IEEE8} & -- & \checkmark  & \checkmark & \checkmark & \checkmark & -- & -- &-- & The aim of this article is to ensure un-interrupted power transmission by diagnosing power lines faults. However, power transmission interruption are dependent vegetation encroachments and faults.   \\ [1ex]
%    \hline
\cite{IEEE9} & -- & --  & -- & -- & \checkmark &\checkmark & \checkmark & -- & The aim of authors in this survey is to provide a strong base for research community to design a system that is able to handel these three tasks: monitoring, control, and diagnosis.  \\ [1ex]
%     \hline

\cite{IEEE10} & -- & --  & -- & -- & \checkmark & \checkmark & \checkmark & -- & The objective of this survey to review remote sensing technologies used for maintenance and monitoring. However, power line inspection is very necessary before maintenance and monitoring.    \\ [1ex]
%    \hline

\cite{IEEE11} & \checkmark & --  & -- & -- &  & -- & -- & -- & The aim of authors is to provide a roadmap for the researcher to design a fully automated power lines inspection system. However, vegetation encroachment is ignored while it is highly related to power lines inspection.    \\ [1ex]
%    \hline

\cite{IEEE12} & \checkmark & --  & -- & -- & -- & -- &\checkmark & -- & The objective of authors is to cover the existing methods for periodical surveillance of power lines to overcome dangerous vegetation encroachment.    \\ [1ex]
%     \hline

\cite{IEEE13} & \checkmark & --  & -- & -- &  & -- & -- & -- & The aim of authors is to provide a roadmap for the researcher to design a fully automated autonomous power lines inspection system having fast and accurate performance.      \\ [1ex]
%     \hline

\cite{IEEE14} & -- & --  & -- & -- & -- & \checkmark & -- & \checkmark & This survey is beneficial for both diagnostic and control engineers to overcome the failures and faults in the power system. However, power lines inspection and fault detection is very necessary for fault diagnosis.     \\ [1ex]
%          \hline

\cite{IEEE16} & \checkmark & --  & -- & -- & -- &-- & -- & \checkmark & The objective of this survey is to review different existing computer vision applications in order to identify a promising technology for power lines management.    \\ [1ex]
\hline
\end{tabular}
\end{table*}


• Please tell us which document class you employ.
– Mico
May 23, 2018 at 11:58
• IEEE transection May 23, 2018 at 11:59
• You are declaring a tabular with 9 columns but some of your rows have 10 columns. May 23, 2018 at 12:04
• It is 9 column materix May 23, 2018 at 12:13
• look at the line it highlights (line 148), it has too many & May 23, 2018 at 12:15

## 1 Answer

The main problem afflicting your table is that it contains 10 columns, whereas your specification of the tabular environment foresees only 9 columns.

In addition to fixing this obvious error, I would suggest you use a tabularx environment, with all but the first column allowing automatic line breaking. In order to make the table fit inside a page, I further suggest you make the middle 8 columns much less wide than the right-hand column. (In the example shown below, the 10th column is six [6!] times as wide as columns 2 thru 9.) Finally, do give your table a more "open look" by (a) getting rid of all vertical bars, (b) providing more whitespace between the rows, and using the line-drawing capabilities of the booktabs package for the remaining few horizontal lines.

With these adjustments adjustments, it's also no longer necessary to use a \tiny font size; \footnotesize will do just fine.

\documentclass{IEEEtran}
\usepackage{tabularx,ragged2e}
\newcolumntype{C}{>{\Centering\arraybackslash\hspace{0pt}}X}
\newcolumntype{L}{>{\RaggedRight\arraybackslash}X}
\usepackage{booktabs} % \toprule, \midrule, \bottomrule, and \addlinespace macros
\usepackage{amssymb} % for '\checkmark' macro
\begin{document}
\begin{table*}[p]

\footnotesize  % "\tiny" is just much too tiny!
\setlength\tabcolsep{3pt} % default: 6pt
\frenchspacing

\caption{Comprehensive analysis of the existing technologies,
specifications, features and critical remarks}
\label{table2}

\begin{tabularx}{\textwidth}{@{} l
*{8}{>{\hsize=0.65\hsize}C} >{\hsize=3.8\hsize}L @{}}
%% 8*0.65+3.8=9 (= # of X-type columns)

\toprule
%% no need to bold-face the header row
Ref. & Line inspection & Fault detection & Fault classifications &
OTLs deterioration problems & Fault localization & Fault diagnosis &
Vegetation encroachment & Monitoring and control & Remarks \\
\midrule

\cite{IEEE2} & -- & \checkmark & \checkmark & \checkmark & -- &-- & -- & -- & The focus of the authors is on the methods used for fault detection, classification, and localization. However, fault diagnosis, monitoring, and controlling of OTLs are ignored.  \\ \addlinespace
\cite{IEEE3}& \checkmark & -- & --  & -- & \checkmark & -- & -- & \checkmark & The aim of this article is threefold: a) review the deterioration problems accompanied with OTLs; 2)~review existing OTLS inspection methods; 3)~design condition monitoring system. However, ignored some crucial factors that significantly effect OTLs.   \\ \addlinespace
\cite{IEEE4} & \checkmark & -- & -- & -- & \checkmark &-- & -- & \checkmark & Authors in this survey highlight gaps in the existing technology used for power lines inspection and provide guidance, how to move forward. However, fault diagnosis, vegetation encroachment, and control aspects of power lines are ignored    \\ \addlinespace
\cite{IEEE5} & -- & \checkmark & \checkmark & \checkmark& \checkmark &-- & -- & -- & The focus of the authors is on fault analysis and fault diagnosis based on intelligent systems. However, the causes of faults are ignored.  \\ \addlinespace
\cite{IEEE6} &  & -- & \checkmark & \checkmark & \checkmark& \checkmark &-- & -- & The authors with support of ESKOM conducted a survey to highlight feasibility of WSN for monitoring and controlling OTLs. However, aspects accompanied with OTLs which compromise monitoring and controlling process are ignored.    \\ \addlinespace
\cite{IEEE7}& -- & \checkmark  & \checkmark & \checkmark & \checkmark & -- & -- &-- & This paper is regarding the faults accompanied with power lines and solutions to overcome faulty situations.  \\ \addlinespace
\cite{IEEE8} & -- & \checkmark  & \checkmark & \checkmark & \checkmark & -- & -- &-- & The aim of this article is to ensure un-interrupted power transmission by diagnosing power lines faults. However, power transmission interruption are dependent vegetation encroachments and faults.    \\ \addlinespace
\cite{IEEE9} & -- & --  & -- & -- & \checkmark &\checkmark & \checkmark & -- & The aim of authors in this survey is to provide a strong base for research community to design a system that is able to handel these three tasks: monitoring, control, and diagnosis.   \\ \addlinespace
\cite{IEEE10} & -- & --  & -- & -- & \checkmark & \checkmark & \checkmark & -- & The objective of this survey to review remote sensing technologies used for maintenance and monitoring. However, power line inspection is very necessary before maintenance and monitoring. \\ \addlinespace
\cite{IEEE11} & \checkmark & --  & -- & -- &  & -- & -- & -- & The aim of authors is to provide a roadmap for the researcher to design a fully automated power lines inspection system. However, vegetation encroachment is ignored while it is highly related to power lines inspection.     \\ \addlinespace
\cite{IEEE12} & \checkmark & --  & -- & -- & -- & -- &\checkmark & -- & The objective of authors is to cover the existing methods for periodical surveillance of power lines to overcome dangerous vegetation encroachment.     \\ \addlinespace
\cite{IEEE13} & \checkmark & --  & -- & -- &  & -- & -- & -- & The aim of authors is to provide a roadmap for the researcher to design a fully automated autonomous power lines inspection system having fast and accurate performance.       \\ \addlinespace
\cite{IEEE14} & -- & --  & -- & -- & -- & \checkmark & -- & \checkmark & This survey is beneficial for both diagnostic and control engineers to overcome the failures and faults in the power system. However, power lines inspection and fault detection is very necessary for fault diagnosis.      \\ \addlinespace
\cite{IEEE16} & \checkmark & --  & -- & -- & -- &-- & -- & \checkmark & The objective of this survey is to review different existing computer vision applications in order to identify a promising technology for power lines management.    \\
\bottomrule
\end{tabularx}
\end{table*}
\end{document}