| For process safety, parallel connection of
a recorder and a temperature transmitter both with burn-out function
is not recommended in a temperature controlled system. The burn-out
circuit of two instruments may interact with each other, causing measurement
errors. There still remains a problem of using a transmitter without
burn-out function in the drawing. If the thermocouple circuit is open
at point A, there
may be no problem since the transmitter may detect the burn-out current
of the recorder and respond to it, driving its output to above 100%.
If the circuit is open at B,
the transmitter cannot detect the burn-out current of the recorder
and the output undesirably changes. |
| We recommend the connections shown in Figure 1 or
2. In Figure1, the recorder and the controller are connected in parallel
to the transmitter output, eliminating all problems discussed above.
In Figure 2, a pair of the thermocouples is used (twin thermocouples).
The recorder and the thermocouple transmitter are individually connected
to each thermocouple. In some critical applications the redundant
system of Figure 2 is used. |
 |
| Figure
1 |
 |
| Figure
2 |
|
| M-System has flexible solutions to meet your
specific application and requirements. Consult our Signal Conditioners
Data Library. |
|
We
need to connect a recorder and thermocouple transmitter in parallel with
the extension wires from a thermocouple. Is there any problem in the connection?
A
block diagram of the parallel connection in question is to the right. It
is a common practice to use a recorder having a burn-out function. If you
use the transmitter output only for temperature monitoring, you may use
a thermocouple transmitter with or without burn-out function together with
a recorder having the function.
