In order to provide more accurate control,
two type "J" thermocouple (T/C) need to be input into one controller.
The controller must use T/C "A" only for sensing until the differential
between T/C "A" and T/C "B" exceeds 45 °F. At this
point, the controller must then switch over to T/C "B" for its
temperature input. Unfortunately, the controller does not have the ability
to make this key T/C exchange by itself.
In order to accomplish this input switching, we will use three M-System
units (2 pcs. M2TS / 1 pc. AYDV) as shown in the figure. The M2TS units
convert the T/C signal to linear 1-5V dc signals which are then fed into
the AYDV deviation alarm unit. The setpoint for the AYDV is set at 10% which
corresponds to the 45°F differential temperature between our T/Cs. By
wiring the positive (+) outputs of each M2TS unit to each pole of the AYDV's
output relay and then wiring the negative (-) outputs together to the negative
(-) side of the controller input, the automatic switching function for the
controller is accomplished when the differential is exceeded. |
