Yokogawa DR240 - Manual (Page 35)

2-14 IM DR231-01E
2.4 Alarm Function
This function will show an alarm on the display or generate an alarm output signal with /A4 or
/R1 option when the measurement conditions of a channel exceed/fall below preset values. Up to
four alarms can be set for each channel.
Type of Alarms
Six types of alarms are available, namely high limit alarm, low limit alarm, high limit on rate-of-
change, low limit on rate-of-change, difference high limit and difference low limit.
Interval for Rate-of-Change Alarms
In case of high/low limit on rate-of-change alarms, variation is measured over a preset interval,
and if the variation exceeds a preset value, an alarm occurs. This interval can be set and applies to
all channels.
Measur-
ement
value
Measured
variation
T
Time
Set interval
1
T 2
t 1 t 2
2 1
Set variation
2 1
T
Time
2
T 1
t 1 t 2
Measur-
ement
value
Measured variation
T –T
t –t
Set interval
2 1 t –t
Set variation
2 1 T –T
•High limit on rate-of-change •Low limit on rate-of-change
Alarm Hysteresis
You can set the width between the value of alarm occurrence and its release. This setting prevents
frequent alarm occurrences/releases in an unstable environment. Hysteresis values can be set in
the 0-1% percentage range of the recording span. The hysteresis setting is used for high and low
limit alarms.
Set alarm
value
Alarm release
Measurement values
Alarm occurrence
1V
Hysteresis
(Approx. 0.5%)
1V
Measurement values Alarm release
Hysteresis (Approx. 0.5%)
Set alarm
value
Alarm occurrence
•High limit alarm •Low limit alarm
Internal Switches
Sixty internal switches are provided which can be operated upon alarm occurrences. These
switches are only for internal operations and are used in combination with the event/action
function (refer to page 2-18).
Alarm Output Relays
If both /A4-option and /R1-option are installed, twelve alarm output relays are provided for
external output.