A boxed unit which lets the 751 (USB) and 851 (Ethernet and Internet) monitor 12 pH electrodes. The electrodes are connected to BNC sockets. You will also need a power supply.
Just connect your electrodes to the pH box's input protected sockets, plug the box into the Microlink 751 or 851 measuring unit and away you go. This method of connection means you can use the same 751 or 851 measuring unit to monitor, for example, temperatures as well as pH.
The reason that you cannot connect pH electrodes directly to the data acquisition unit is that they have a very high output impedance and are not able to supply enouch current to allow the use of a normal voltage input. The pH connection box has high impedance amplifiers to condition the signals from the electrodes. The pH box connects by a ribbon cable to the 751 or 851 unit. It also provides screw terminals for any other signals you are monitoring.