How to find peak value using FFT

Hello,

My question is how to find the time-domain peak value (magnitude) of a signal in frequency domain.

So far, I have applied FFT to a collection of sampled data in the attached CSV file. The collected data has the following information:

• signal length is 30 seconds
• signal was sampled at 1kHz
• signal contains the magnitude of almost 0.14 amps @15.8 Hz and 0.12 amps @16 Hz according to the attached image in time domain

Could anyone advise how to locate the above peaks with its corresponding frequencies in frequency domain?

The following is the code that I did so far:

filename = 'FFT_Case_1.4_A.csv';
signal = csvread(filename);

N = length(signal); % defines the total number of signal array
fax_bins = [0:N-1]; % fix the x-axis with the starting point of 0
half_N = ceil(N/2); % get the half number of samples for single side plot
fs = 1000; % sampling frequency of signal
fnyquist = fs/2; % Nyquist frequency of signal

signal_mag = 2*abs(fft(signal)/N); % magnitude of signals after transform
fax_Hz = fax_bins*fs/N; % convert bins to Hz using simple formula

plot(fax_Hz(1:half_N), signal_mag(1:half_N))
xlim([1 51])
title('Single-side Magnitude Spectrum')
xlabel('Frequency (Hz)')
ylabel('Magnitude (Amps)');

Any advice is most appreciated. Thanks.

Kind regards, Thomas