Get the beam energy in kev, based on typical biases: 
                itw (or ite bias) - bias15 - platform bias
                
            if get_error: fetch error in value, rather than value

def beam_kev(self,get_error=False):
        """
            Get the beam energy in kev, based on typical biases: 
                itw (or ite bias) - bias15 - platform bias
                
            if get_error: fetch error in value, rather than value
        """
        
        # get epics pointer
        epics = self.epics
        
        # fetch stds
        if get_error:
            attr = 'std'
        else:
            attr = 'mean'
        
        # get inital beam energy in keV
        beam = getattr(epics.target_bias,attr)/1000.
            
        # get RB cell voltage
        bias15 = getattr(epics.bias15,attr)/1000.
        
        # get platform bias 
        if self.area == 'BNMR':
            platform = getattr(epics.nmr_bias,attr)
        elif self.area == 'BNQR':
            platform = getattr(epics.nqr_bias,attr)/1000.
        else:
            raise RuntimeError('Area not recognized')
        
        if get_error:
            return np.sqrt(np.sum(np.square((beam,bias15,platform)))) # keV
        else:
            return beam-bias15-platform