The Walchem WPHWDP series controller is now obsolete and has been replaced by the WPH600 series controller. The new series has upgraded features; for reference, here is the description of the old series:
pH ORP Controller: Single or Dual
Control Relays: On/off or pulse proportioning
Output: 4-20mA
Single Input (WPH) or Dual Input (WDP) pH Controller available with pH and/or ORP electrodes, powered relays, alarm relay and pulse outputs.
