AI-Tek Instruments TACHTROL 3, Instruction Manual, Page: 12 / 30

Full Scale
You can determine at which value of the analog function the analog output delivers 20
milllamps to the load.
Note:
The 0-20mA can be converted to a 0 to 5vdc or 0 to 10vdc signal by placing a resistor
across the input of the receiving instrument whose parallel combination with the input resist-
ance of the receiver is 250 ohms or 500 ohms respectively.
4.3.3 Setpoints
Relay setpolnts are used to trigger events. In some applications, they are used to trigger the
adding of ingredients at specified stages of a process. In other applications, they are used to
trigger alarm conditions. For Instance, they are used to trigger an alarm condition when the
speed of a machine drops below or rises above its normal range of operation. The following dis-
cussion will focus on the latter type of application.
Setpoint Types
There are two types of setpoints: underspeed and overspeed. Underspeed relays trigger events
when frequency drops below the setpolnt.
FIGURE 2. UNDERSPEED SETPOINT
Overspeed relays trigger events when the frequency rises above the setpolnt.
FIGURE 3. OVERSPEED SETPOINT
Setpoint Behavior
Relay setpoints may be configured to either energize or de-energize above and below the set-
point value. Thus, for each relay setpoint you must decide what type you want and how you
want the relay to behave. Overspeed relays which energize above the setpoint and under-
speed relays which energize below the setpoint are called Non-Failsafe. Ovespeed relays which
de-energize above the setpoint and underspeed relays which de-energize below the setpoint
are called Failsafe. Failsafe provides you with a warning in the event that a power failure occurs
which the machine is operating within the Non-Alarm (Safe) area of operation.
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