diff --git a/pyFTS/data/artificial.py b/pyFTS/data/artificial.py
index 4b4eaee..7a80082 100644
--- a/pyFTS/data/artificial.py
+++ b/pyFTS/data/artificial.py
@@ -49,7 +49,7 @@ def generate_linear_periodic_gaussian(period, mu_min, sigma_min, mu_max, sigma_m
     :return:
     """
 
-    if period > num:
+    if period > it:
         raise("The 'period' parameter must be lesser than 'it' parameter")
 
     mu_inc = (mu_max - mu_min)/period
@@ -73,6 +73,8 @@ def generate_linear_periodic_gaussian(period, mu_min, sigma_min, mu_max, sigma_m
         mu += (mu_inc if signal else -mu_inc)
         sigma += (sigma_inc if signal else -sigma_inc)
 
+        sigma = max(sigma, 0.005)
+
     return ret
 
 
@@ -105,8 +107,10 @@ def generate_senoidal_periodic_gaussian(period, mu_min, sigma_min, mu_max, sigma
             tmp = np.minimum(np.full(num, vmax), tmp)
         ret.extend(tmp)
 
-        mu += mu_range * np.sin (period * k)
-        sigma += mu_range * np.sin (period * k)
+        mu += mu_range * np.sin(period * k)
+        sigma += sigma_range * np.sin(period * k)
+
+        sigma = max(sigma, 0.005)
 
     return ret
 
@@ -169,6 +173,8 @@ def _append(additive, start, before, new):
 
         if l2 < l1:
             new.extend(np.zeros(l1 - l2).tolist())
+        elif 0 < l1 < l2:
+            new = new[:l1]
 
         if len(before) == 0:
             tmp = np.array(new)
@@ -275,11 +281,11 @@ class SignalEmulator(object):
                 tmp = generate_gaussian_linear(0, 0, parameters['mu'], parameters['sigma'],
                                          it=num, num=1, vmin=vmin, vmax=vmax)
             elif component['type'] == 'periodic':
-                period = component['period']
+                period = parameters['period']
                 mu_min, sigma_min = parameters['mu_min'],parameters['sigma_min']
                 mu_max, sigma_max = parameters['mu_max'],parameters['sigma_max']
 
-                if parameters['type'] == 'senoidal':
+                if parameters['type'] == 'sinoidal':
                     tmp = generate_senoidal_periodic_gaussian(period, mu_min, sigma_min, mu_max, sigma_max,
                                                         it=num, num=1, vmin=vmin, vmax=vmax)
                 else:
@@ -300,7 +306,6 @@ class SignalEmulator(object):
                 start = np.random.randint(0, len(signal))
                 tmp = [_mx] if np.random.rand() >= .5 else [-_mn]
 
-
             last_num = num
             last_it = it
 
diff --git a/pyFTS/tests/general.py b/pyFTS/tests/general.py
index 8b036bc..b3f4e9f 100644
--- a/pyFTS/tests/general.py
+++ b/pyFTS/tests/general.py
@@ -16,10 +16,17 @@ from pyFTS.common import Transformations, Membership
 
 from pyFTS.data import artificial
 
+"""
 cd = artificial.SignalEmulator()\
     .stationary_gaussian(0,.2,length=10, it=1)\
     .incremental_gaussian(0.5, 0,start=5,length=5)\
     .blip()\
     .stationary_gaussian(3,.2,length=10, it=1, additive=False)
 print([round(k,3) for k in cd.run()])
+"""
 
+signal = artificial.SignalEmulator()\
+    .stationary_gaussian(1,0.2,length=130,it=10)\
+    .periodic_gaussian('sinoidal',100, 0.5,0.5,10,1,start=100,length=2000)\
+    .blip()\
+    .run()