diff --git a/example.py b/example.py
index 5facd6c..bfdecce 100644
--- a/example.py
+++ b/example.py
@@ -1,5 +1,6 @@
 import tdm_ripper
 import numpy as np
+import matplotlib.pyplot as plt
 
 tdmpath = b"samples/SineData.tdm"
 tdxpath = b"samples/SineData.tdx"
@@ -17,6 +18,27 @@ print(RP.num_groups())
 RP.print_channel(1,b"SineData_extract.dat")
 
 # extract channel and return it to numpy array
-chann = RP.get_channel(1)
+channels = RP.get_channel(1)
+Nlen = len(channels)
+channels = np.append(channels,RP.get_channel(2))
+channels = np.append(channels,RP.get_channel(3))
+channels = np.append(channels,RP.get_channel(4))
+channels = np.append(channels,RP.get_channel(5))
+channels = np.append(channels,RP.get_channel(6))
+channels = np.append(channels,RP.get_channel(7))
+channels = np.append(channels,RP.get_channel(8))
+print(channels.shape)
+print("\n\n")
+print(channels[0:40])
 
-print(dim(chann))
+x = np.linspace(0,Nlen,Nlen)
+plt.plot(x,channels[0:1000])
+plt.plot(x,channels[1000:2000])
+plt.plot(x,channels[2000:3000])
+plt.plot(x,channels[3000:4000])
+plt.plot(x,channels[4000:5000])
+plt.plot(x,channels[5000:6000])
+plt.plot(x,channels[6000:7000])
+plt.plot(x,channels[7000:8000])
+plt.grid()
+plt.show()
diff --git a/lib/tdm_ripper.cpp b/lib/tdm_ripper.cpp
index 8c29fa4..21133b7 100644
--- a/lib/tdm_ripper.cpp
+++ b/lib/tdm_ripper.cpp
@@ -278,6 +278,8 @@ std::vector<double> tdm_ripper::get_channel(int channelid)
 
 void tdm_ripper::print_channel(int channelid, const char* filename, int width)
 {
+  assert( channelid > 0 && channelid <= num_channels_ && "please provide valid channel id" );
+
   std::ofstream fout(filename);
 
   std::vector<double> channdat = get_channel(channelid);
diff --git a/pytdm_ripper.pyx b/pytdm_ripper.pyx
index 153e90b..e0f5498 100644
--- a/pytdm_ripper.pyx
+++ b/pytdm_ripper.pyx
@@ -2,6 +2,7 @@
 # distutils: language = c++
 
 from tdm_ripper cimport tdm_ripper
+import numpy as np
 
 cdef class pytdmripper:
 
@@ -24,7 +25,7 @@ cdef class pytdmripper:
         return self.cripp.num_groups()
 
     def get_channel(self, int channelid):
-        return self.cripp.get_channel(channelid)
+        return np.asarray(self.cripp.get_channel(channelid))
 
     def print_channel(self, int channelid, const char* filename):
         self.cripp.print_channel(channelid,filename)