Some years ago Bircher discontinued the LD series (formerly SD series) of loop detectors and while the demand for replacement units is not as great, we are committed to supporting these products through the ProLoop range of loop detectors.
Below is a list that cross references the LD part numbers to the appropriate ProLoop unit. If you cannot find a cross reference for the part you 
require, then a standard ProLoop 11 pin version will still be a suitable replacement as these newer models are fully programmable. If you need any assistance, please give us a call on 01495 360022.
Single loop detector with 2 relays operating at 24Vac/dc:
LD20.0.A4.24ADC, LD20.0.B3.24ADC, LD20.0.H9.24ADC, LD20.0.N2.24ADC, LD20.1.A1.24ADC, LD20.1.A3.24ADC, LD20.1.B3.24ADC, LD20.1.B4.24ADC, LD20.1.H6.24ADC, LD20.1.H9.24ADC, LD20.1.N1.24ADC, LD20.1.N2.24ADC, LD20.2.A1.24ADC, LD20.2.B5.24ADC, LD20.2.H9.24ADC, LD20.2.N2.24ADC, LD20.3.H9.24ADC, LD20.X.H9.24ADC, LD21.0.B3.24ADC, LD21.0.H9.24ADC, LD21.0.N2.24ADC, LD21.1.A5.24ADC, LD21.1.H6.24ADC, LD21.1.H9.24ADC, LD21.2.H9.24ADC, LD21.2.N2.24ADC, LD21.3.B4.24ADC, LD21.3.H9.24ADC, LD21.X.H9.24ADC, LD22.0.H9.24ADC, LD22.1.H6.24ADC, LD22.1.H9.24ADC, LD22.1.N2.24ADC, LD22.2.H9.24ADC, LD23.0.H9.24ADC, LD23.1.B3.24ADC, LD23.1.H9.24ADC, LD23.3.B3.24ADC, LD23.3.N2.24ADC, LD24.0.H9.24ADC, LD24.1.H9.24ADC, LD24.2.H9.24ADC, LD24.2.N2.24ADC, replace with model number 299855.
Single loop detector with 2 relays operating at 115Vac:
LD20.0.H9.115AC, LD20.1.H9.115AC, LD20.2.N1.115AC, LD21.1.H9.115AC, LD22.0.H9.115AC, LD22.1.H9.115AC, LD22.2.H9.115AC, LD23.1.A3.115AC, LD23.1.H9.115AC, replace with model number 224481.
Single loop detector with 2 relays operating at 230Vac:
LD20.0.B3.230AC, LD20.0.H9.230AC, LD20.0.N2.230AC, LD20.1.A1.230AC, LD20.1.A2.230AC, LD20.1.A3.230AC, LD20.1.B3.230AC, LD20.1.B4.230AC, LD20.1.B5.230AC, LD20.1.H6.230AC, LD20.1.H9.230AC, LD20.1.N1.230AC, LD20.1.N2.230AC, LD20.2.B4.230AC, LD20.2.B5.230AC, LD20.2.H9.230AC, LD20.2.N2.230AC, LD20.3.H9.230AC, LD20.X.H9.230AC, LD21.0.H9.230AC, LD21.1.A1.230AC, LD21.1.H9.230AC, LD21.1.N1.230AC, LD21.1.N2.230AC, LD21.2.A2.230AC, LD21.2.B3.230AC, LD21.2.H9.230AC, LD21.2.N2.230AC, LD21.3.H9.230AC, LD21.X.H9.230AC, LD22.0.H9.230AC, LD22.1.B3.230AC, LD22.1.H9.230AC, LD22.1.N2.230AC, LD22.2.H9.230AC, LD23.0.H9.230AC, LD23.1.H9.230AC, LD23.2.H9.230AC, LD23.3.H9.230AC, LD24.0.H9.230AC, LD24.1.H9.230AC, LD24.2.H9.230VAC, replace with model number 224482.
Dual loop detector with 2 relays operating at 24Vac/dc:
LD40.0.B3.24ADC, LD40.0.H9.24ADC, LD40.0.N5.24ADC, LD40.0.N6.24ADC, LD40.1.A1.24ADC, LD40.1.A2.24ADC, LD40.1.B3.24ADC, LD40.1.B4.24ADC, LD40.1.H6.24ADC, LD40.1.H9.24ADC, LD40.1.N1.24ADC, LD40.2.A1.24ADC, LD40.2.B3.24ADC, LD40.2.H9.24ADC, LD40.2.N2.24ADC, LD40.3.H9.24ADC, LD40.4.R0.24ADC, LD40.X.H9.24ADC, replace with model number 299858.
Dual loop detector with 2 relays operating at 115Vac:
LD40.1.B4.115AC, LD40.1.H6.115AC, LD40.1.H9.115AC, LD40.3.B4.115AC, replace with model number 224484.
Dual loop detector with 2 relays operating at 230Vac:
LD40.0.B3.230AC, LD40.0.H9.230AC, LD40.0.N2.230AC, LD40.1.B3.230AC, LD40.1.B4.230AC, LD40.1.B5.230AC, LD40.1.H9.230AC, LD40.1.N1.230AC, LD40.1.N2.230AC, LD40.2.B4.230AC, LD40.2.H9.230AC, LD40.2.N2.230AC, LD40.3.H9.230AC, LD40.4.R0.230AC, LD40.X.H9.230AC, replace with model number 224485.