Do you want to learn more about machine and equipment alarm commands? The World of Electrical in this article teaches step by step how to make an electrical command to alarm machines and equipment, where it is possible to silence the siren and remain with the signal signaled, indicating the fault as long as it persists.
The alarm command for a machine is very common in industrial environments, so the professional in the World of Electrical will certainly come across alarm commands for machines several times.
Cala siren – Main components
There are two components that are fundamental for the operation of the siren shutdown command, that of the overload relay and the audible alarm itself.
Main components – Overload relay
The overload relay is a component that has the function of protecting the machine’s motor against the increase of current. When the overload relay identifies this increase in electrical current, the relay immediately activates the emergency contacts, switching the contacts. In overload relays, we have a contact normally closed with the numbering 95-96 and another contact normally opens with the numbering 97-98.
Any motor command the normally closed contact 95-96 is used to cut the seal that feeds the contractor, that is, as soon as the overload relay is automatically activated, the motor is switched off. It is important to note that in electrical commands, the contact NF 95-96 is always used at the beginning of the command line.
Many professionals in the Electrical Industry have already assembled a command with an overload relay, have seen or used this contact, but few have used the normally open contact 97-98, which in the case of this alarm command is essential.
Main components – Audible alarm
The second element is the audible alarm itself and its operation is very simple when the alarm receives voltage it emits an audible signal and its LED lights up, indicating a fault alarm.
Cala sirene – Operation
We present an alarm command for an engine start with a quiet alarm button, popularly known as the siren shut. We simulate an overload on the overload relay by pressing the test button and at this moment the audible alarm goes off and at the same time the yellow LED lights up indicating the fault.
To silence the siren just press the yellow button, integrated with the yellow signal, which is a signaled command button. We can see that the yellow signal is only turned off when I clear the fault, press the reset button of the overload relay.
The idea of this command is that when a fault triggers the alarm, the operator can silence the alarm while maintenance is being carried out, however, throughout the time the fault is occurring, the yellow LED remains on.
A detail worth noting in this command is that we did it using a remote control, that is, the buttons that control the machine are installed away from the control panel, as in a control room for example.
In this coma we made the interconnection of the contactors, circuit breaker and overload relay to the buttons and alarm with an interruption by terminals, where a cable harness leaves the terminals and goes to the buttons and the audible alarm.
Cala siren – Electrical diagram
Let’s analyze the command diagram that appears in the image below to understand how this alarm silence function works. As we can see in this diagram there are four lines, where the first line is a common direct start that uses a push button with a seal contact.
An auxiliary contactor is connected to the second line. Note that the first contacts on both line 1 and line 2 are overload relay contacts. Line 1 is the normally closed contact 95-96 and line 2 is the normally open contact 97-98.
When a fault occurs, two things will happen at the same time, in line 1 the contact NC 95-96 opens and the main contactor seal is interrupted, and the main contactor is automatically switched off. The second thing that will happen is that on line two, contact NF 97-98 will close and activate the auxiliary contactor.
The first contact of line 3 and line 4 are normally open contacts of the auxiliary contactor. After activating the auxiliary contactor, these open contacts will be closed.
Inline three, after closing the contacts, the yellow signal will be activated indicating the fault. Inline four we have a normally closed contact of the second auxiliary contactor, which after closing the contacts, the line will be completely closed and the audible alarm is also triggered.
See that inline 4 there is a branch, where a push button is located to silence the siren. When the button to silence the siren is pressed, the second auxiliary contactor is activated, closing the second seal contact and with the second auxiliary contactor closed, the audible alarm contact opens and the siren shuts off, thus even with the siren the light that indicates an alarm is still on.
The light only goes out when contact 97-98 of the overload relay opens, that is, when the fault is cleared from the relay. This type of command can be found on any machine with an alarm system through electrical commands.