ALARM Command

Applies to: ALL modes (general purpose).

The CT-BOX can detect when the measured current is outside a desired current range. The command that configures this functionality is ALARM.

The alarm check is performed once for every output value, so the check rate is equal to the output data frequency set by:

the TS setting in OSC mode;
the FREQ setting in DLOG mode;
the DMM:FREQ and DMM:NOP settings in DMM mode.

Example(s):

Mode	Setting	Output data frequency	Alarm checked every
OSC	`TS:1000`	1 kHz	1 ms
DLOG	`FREQ:1`	1 Hz	1 s
DMM	`DMM:FREQ:50`, `DMM:NOP:10`	5 Hz	200 ms

Command Format:

R/W	Command	Response	Description
W	`ALARM:ON`	`ACK` / `NAK:x`	Enable the alarm check functionality
W	`ALARM:OFF`	`ACK` / `NAK:x`	Disable the alarm check functionality
W	`ALARM:CLR`	`ACK` / `NAK:x`	Clear the alarm condition
R	`ALARM:?`	`ON` / `OFF`	Read the alarm check setting

Threshold Configuration

Command Format:

R/W	Command	Response	Description
W	`ALARM:ULIM:<current>`	`ACK` / `NAK:x`	Set the upper limit current threshold
R	`ALARM:ULIM:?`	`<current>`	Read the upper limit current threshold
W	`ALARM:LLIM:<current>`	`ACK` / `NAK:x`	Set the lower limit current threshold
R	`ALARM:LLIM:?`	`<current>`	Read the lower limit current threshold

Parameter(s):

Name	Type	Allowed values	Default	Description
`<current>` for ULIM	float	-1200.0 – 1200.0	1200.0	Upper current threshold in Ampere [A]
`<current>` for LLIM	float	-1200.0 – 1200.0	-1200.0	Lower current threshold in Ampere [A]

LLIM must always be lower than ULIM. A command that would set LLIM ≥ ULIM is rejected with NAK:2.

Alarm Behaviour

The alarm checking is performed only when the acquisition is enabled (ACQ:ON). When the acquired current is outside the configured range, the alarm condition is set. In this condition:

the Alarm line of the D-SUB DA-15S (female) connector is driven high;
the magnetic relay is switched, so its Normally Open contact (Relay NO) closes.

For the connector pinout, refer to the CT-BOX User’s Manual.

The alarm condition is also reported on the Status Register:

the Alarm flag bit indicates the alarm condition (0 = no alarm; 1 = alarm condition);
the Alarm Direction bit indicates the alarm direction (0 = detected a current under the LLIM; 1 = detected a current over the ULIM).

Important

Whenever the alarm condition occurs, it is latched: the Alarm flag bit in the Status register and the Alarm line stay set even after the current returns inside the configured range. The relay is driven by the Alarm line, so it also stays switched. Only the command ALARM:CLR clears the alarm condition, the Alarm flag bit and the Alarm line, and switches the relay back.

Example(s):

Enable the alarm checking:

ALARM:ON
ACK

Set the upper threshold limit to 100 A:

ALARM:ULIM:100
ACK

ALARM:ULIM:?
100