- Use the XIC instruction in your ladder logic to determine if a bit is ON.
- Use an XIO instruction in your ladder logic to determine if a bit if off.
- Use OTE instruction in your ladder logic to turn on a bit when rung condition is evaluated as true.
Example 1
Lets construction a simple circuit with one switch as a contact and one output as a coil. When the switch is on the light will go on and when the switch is off the light will turn off.
Input / Output
- Switch I: 1.0/0
- Light O: 2.0/0
Ladder Logic Solution
When the switch is on the input Address: I:1.0/0 will be on and hence the rung will be energized hence the outputs on address O:2.0/0 will be energize and the light will go on.
When the switch is off the rung will be de-energized and the light will go off.
Example 2
Lets build an alarm system. Let's assume that we have 3 signals (Inputs) that we get from the field that warn us about some kind of fire danger.
- Any 1 signal, turn the warning light on;
- Any 2 signals will sound the siren.
- All 3 signals, will start the water spray system
Input / Output
- Alarm 1 I:1.0/7
- Alarm 2 I:1.0/8
- Alarm 3 I1.0/9
- Siren O:2.0/7
- Alarm Light O:2.0/8
- Spray System O:2.0/9
Ladder Logic Solution
We put all the alarm signals in parallel. This is equivalent to an or statement. This means that when either Alarm1 or Alarm2 or Alarm3 becomes on the rung will be energized and hence the Fire light will be turned on. This does not take care of the count of the alarms. It only look at whatever alarm is on.
Here we put every possible combination of 2 alarms in a separate line. This is equivalent to an end statement. (Alarm1 and Alarm2) or (Alarm1 and Alarm3) or This takes care of 2 alarms at a time in which case if any of these combinations becomes true the Fire siren will go on.
As you can see the 2 alarms are in series. This is equivalent to an and statement. Which is (Alarm1 and Alarm2 and Alarm3) if and only if alarm1 and alarm2 and alarm3 are on (3 of them) it is only then that the fire spray will be turned on.
Note
- · Contacts in parallel are equivalent to an OR statement
- · Contacts in series are equivalent to an AND statement
