diff --git a/hb3a_geometry.py b/hb3a_geometry.py
new file mode 100644
index 0000000..a9e614d
--- /dev/null
+++ b/hb3a_geometry.py
@@ -0,0 +1,167 @@
+import sys
+import datetime
+import helper
+
+# Definition of constants
+HB3A_L1 = 2.
+
+
+class HB3AGeometry(helper.MantidGeom):
+    """
+    HB3A geometry extended from MantidGeom
+    """
+    def __init__(self, instname, comment=None, valid_from=None, valid_to=None):
+        """
+        initialization
+        :param instname: name of instrument
+        :param comment: comment
+        :param valid_from: beginning date
+        :param valid_to: end date
+        """
+        super(HB3AGeometry, self).__init__(instname, comment, valid_from, valid_to)
+
+        return
+
+# END-DEF-HB3A
+
+
+def generate_1_panel_idf(out_file_name):
+    """ Generate the 1 panel (256 X 256) IDF valid to October 2018
+    :return:
+    """
+    # generate instrument geometry object
+    instrument_name = 'HB3A'
+    authors = ["Wenduo Zhou"]
+    begin_date = '2015-01-01 00:00:01'
+    end_date = '2018-10-20 23:59:59'
+
+    # boiler plate stuff
+    hb3a = HB3AGeometry(instrument_name,
+                        comment="Created by " + ", ".join(authors),
+                        valid_from=begin_date,
+                        valid_to=end_date)
+
+    hb3a.addComment('DEFAULTS')
+    hb3a.addHfirDefaults()
+
+    # source
+    hb3a.addComment("SOURCE")
+    hb3a.addModerator(HB3A_L1)
+    # sample
+    hb3a.addComment("SAMPLE")
+    hb3a.addSamplePosition()
+    # monitor
+    hb3a.addComment("MONITORS")
+    hb3a.add_monitor_type()
+    # self._vulcan.addMonitors(distance=[-1.5077], names=["monitor1"])
+
+    # add detectors
+    hb3a.addComment('Define detector banks')
+    hb3a.addComponent(type_name='detectors', idlist='detectors')
+    # define detector type
+    hb3a.add_banks_type(name='detectors',
+                        components=['bank1'])
+
+    # define center bank
+    hb3a.addComment('Define Centre Bank')
+    hb3a.add_bank(name='bank1', component_name='square256detector',
+                  x=2.0, y=0., z=0., rot=90)
+
+    # 20 x 8 packs
+    hb3a.addComment('256 x 256 pack')
+    hb3a.angler_detector(name='square256detector', num_linear_pixel=256, tube_x=0.01)
+
+    # write file
+    hb3a.writeGeom(out_file_name)
+
+    return
+
+
+def generate_3_panel_idf(out_file_name):
+    """
+    generate 3 panel (3 x 4 x 256 x 256) instrument definition for 2018 October
+    upgrade
+    :return:
+    """
+    # generate instrument geometry object
+    instrument_name = 'HB3A'
+    authors = ["Wenduo Zhou"]
+    begin_date = '2018-10-20 23:59:59'
+    end_date = '3018-10-20 23:59:59'
+
+    # boiler plate stuff
+    hb3a = HB3AGeometry(instrument_name,
+                        comment="Created by " + ", ".join(authors),
+                        valid_from=begin_date,
+                        valid_to=end_date)
+
+    hb3a.addComment('DEFAULTS')
+    hb3a.addHfirDefaults()
+
+    # source
+    hb3a.addComment("SOURCE")
+    hb3a.addModerator(HB3A_L1)
+    # sample
+    hb3a.addComment("SAMPLE")
+    hb3a.addSamplePosition()
+    # monitor
+    hb3a.addComment("MONITORS")
+    hb3a.add_monitor_type()
+    # self._vulcan.addMonitors(distance=[-1.5077], names=["monitor1"])
+
+    # add detectors
+    hb3a.addComment('Define detector banks')
+    hb3a.addComponent(type_name='detectors', idlist='detectors')
+    # define detector type
+    hb3a.add_banks_type(name='detectors',
+                        components=['bank1', 'bank2', 'bank3'])
+
+    # define center bank
+    hb3a.addComment('Define Centre Bank')
+    hb3a.add_bank(name='bank3', component_name='square256detector',
+                  x=2.0, y=0., z=0., rot=90)
+
+    # define upper bank
+    hb3a.addComment('Define Upper Bank')
+    hb3a.add_bank(name='bank3', component_name='square256detector',
+                  x=2.0, y=1., z=0., rot=90)
+
+    # define lower bank
+    hb3a.addComment('Define Lower Bank')
+    hb3a.add_bank(name='bank1', component_name='square256detector',
+                  x=2.0, y=-1., z=0., rot=90)
+
+    # 512 x 512 pack
+    hb3a.addComment('512 x 512 pack')
+    hb3a.angler_detector(name='square256detector', num_linear_pixel=512, tube_x=0.01)
+
+    #
+    hb3a.writeGeom(out_file_name)
+
+    return
+
+
+def main(argv):
+    """ Main
+    :param argv:
+    :return:
+    """
+    if len(argv) < 2:
+        print ('Generate HB3A IDF: {} [number of panel (1 or 3)')
+        sys.exit(0)
+
+    num_panel = int(argv[1])
+    now = datetime.datetime.now()
+    output_idf_name = 'HB3A_Definition_{:04}{:02}{:02}_{:02}{:02}.xml' \
+                      ''.format(now.year, now.month, now.day,
+                                now.hour, now.minute)
+    if num_panel == 1:
+        generate_1_panel_idf(output_idf_name)
+    elif num_panel:
+        generate_3_panel_idf(output_idf_name)
+
+    return
+
+
+if __name__ == '__main__':
+    main(sys.argv)