Add Boonton 4240 RF power meter driver (#50)

* Added draft Booton 4240 RF PM driver

* Tested Boonton 4240 RF PM driver

lightlab/equipment/lab_instruments/Boonton_4240_PM.py

@@ -0,0 +1,41 @@
+import time
+from . import VISAInstrumentDriver
+
+class Boonton_4240_PM(VISAInstrumentDriver):
+    """ Boonton 4240 (4242) Two-Channel RF Power Meter
+
+        `Manual: <https://boonton.com/portals/0/products/rf%20power%20meters/4240/4240_instructionmanual.pdf>`__
+    """
+
+    def __init__(self, name="Booton 4240 PM", address=None, **kwargs):
+        VISAInstrumentDriver.__init__(self, name=name, address=address, **kwargs)
+
+    def reset(self):
+        return self.write("*RST")
+
+    def getID(self):
+       return self.query("*IDN?")
+
+    def getFilterTime(self, channel=1):
+        return float(self.query(f"SENS{channel}:FILT:TIM?"))
+
+    def setFilterTime(self, time=0.05, channel=1):
+        self.write(f"SENS{channel}:FILT:TIM {time}")
+
+    # Note: this function fails for filter times beyond 1. More investigation required
+    def read(self, channel=1):
+        for i in range(3):
+            try:
+                response = self.query(f"READ{channel}:CW:POW?")
+                break
+            except:
+                pass
+
+        splitted = response.split(",")
+        if len(splitted) == 2:
+            channel = int(splitted[0])
+            power = float(splitted[1])
+            return power
+        return -99.99
+
+