Instructions

UM-0085-B09 DT80 Range User Manual Page 375

Part P – The CEM20

Figure 172: A CEM20 module (left), shown connected to a DT80

What is the CEM20?

The dataTaker CEM20 (Channel Expansion Module) is an analog multiplexer specially designed to work with DT80

series data loggers. Each CEM20 provides 20 additional analog channels. Up to five CEM20s can be connected to a

DT80 and sixteen to a DT85, giving a total of 100 and 320 analog input channels respectively.

The CEM20 contains relay multiplexers which connect the selected channel through to one of the DT80's analog inputs.

In order to measure a sensor connected to a CEM20 input:

1. The DT80 will first send a command to the appropriate CEM20, which will cause it to connect the required input

through to its analog output terminals.

2. The CEM20's analog output terminals are wired to one of the DT80's analog input channels, so the DT80 will

then simply perform a normal analog measurement on the appropriate channel.

Measuring a sensor connected to a CEM20 channel is therefore just like measuring one that is directly connected to the

DT80. The main difference is that the measurement will take longer (typically about twice as long) due to the extra step

involved.

Note: the CEM20 is not supported on DT82E and DT82I models, or on any Series 1 model.

Connecting CEM20s

As shown in the photograph above, there are two main connections to each CEM20, namely:

• A 4-wire power/control connection (the upper cable in the photograph). This cable connects to the DT80's

switched 12V power output in order to supply power to the CEM. The cable also contains two control signals,

which are driven by two of the DT80's digital outputs: 5D and 6D.

• A 4-wire analog connection. This connects the analog output of the CEM20 to one of the DT80's analog inputs.

Each CEM20 connects to a separate analog input on the logger. (Thus for every CEM20 that you connect, you

gain 20 analog inputs but lose one analog input on the logger.)

The photograph shows a single CEM20. To connect a second CEM20:

• Each CEM20 includes a power/control output terminal block, located directly above the power/control input. This

can be used to "daisy chain" the power and control signals to the next CEM20.

• The analog output of the second CEM20 then connects to the second analog input on the DT80, in the same

way as the first CEM20, which connects to the first analog input.