Dissolved Oxygen Controller Operation
Teledyne Analytical Instruments 37
output field for each channel. The manual mode assignment allows the
percent output display to be associated with any of the 4-20 outputs, in-
cluding the HART output. When in the manual mode the 4-20 output is
controlled from the keyboard. Zero percent corresponds to a current of 4
mA, and 100 percent corresponds to a current of 20 mA. If a 4-20 output
is used to control the process then the manual mode is normally assigned
to that output, although the instrument does not require this choice.
Cross-channel assignments are allowed in that the selected 4-20 can be
assigned to something on the other channel. Cross-channel assignments can
usually be avoided, and they should be avoided when possible.
To change the assignment simultaneously depress both
CALIBRATE ◄/ ► keys, then use the right-side CALIBRATE ▲/▼
keys to change the selection. One of the selections is “none”, and with
that selection the percent output field is not present in the operational
display. The bottom line shows the signal that the selected 4-20 is
assigned to. On two channel instruments the next display is the manual
mode assignment for channel two.
Each 4-20 output can have only one manual mode control assigned
to it. If one already exists for the current selection it will be preceded by
a question mark. Some instruments have more than two manual mode
controls in the operational displays, and they must all he assigned to
different 4-20 outputs if they are activated.
The other manual mode controls are built-in in some instruments.
An example would he the weight-percent display of a co nductivity unit.
The manual m ode field appea rs in a separate display in these cases, and
it is independent of the manual mode assignments for the main display.
The manual mode capability is automatically activated when a 4-20 is
assigned to one of these fu nctions. The pe rcent output field does not
appear in the operational display unless a 4-20 is assigned to it.
Conversely, when changing the 4-20 assignments a conflict c an
arise if a 4 -20 with a pre- existing manual mode control is reassigned to
ch1 man mode on 4-20:
3 (ch1 PV)