Teco SG2 v3 PLR
Two weeks after our latest family addition was born, my wife began to reach a level of tiredness that can only be obtained after two weeks of nursing constantly with little bits of sleep here and there. While feeding our child at night, my wife was having a difficult time being able to time 15 minutes with the clock. I searched for commercial products which were simple timers that could be preset with large buttons and obvious indicators as to the timer’s state. I came-up empty, so I made my own.
The Players:
- Teco SG2 12HR-12D v3 PLR (programmable logic relay) and its DC power supply
- Automation Direct illuminated combination start / stop station
What I needed was simple: a timer that was preset to 15 minutes, capable of being paused, easy to reset, and which had an indicator that clearly showed the state of the timer. The easiest way I could think of accomplishing this was to use my trusty Teco SG2 PLR and a combination start / stop station with a built-in indicator.
Starting with the wiring, I connected the start and stop switches as inputs to the Teco, and connected the indicator to the first output. I drew-up a quick design, listing the major states of the timer, how they would be enabled, and how they would be indicated.
Quick Design Overview:
- Timer not enabled, no indicator, activated by the red button if timing or paused (reset)
Start / Stop Station
- Timer timing, steady indicator, activated by the green button if paused or not enabled
- Timer paused, slowly blinking indicator, activated by the green button once timing has commenced
- Timer done, fast blinking indicator, activated when the internal timer is done (16 minutes = 15 mins. feeding + 1 min. for “setup”)
The following shows the actual ladder logic program I used for this timer. It is quite simple, using the two switch inputs (I01 & I02) and one indicator light output (Q01) on the start / stop combo, which comprises all of the external inputs and outputs. M01 is an internal timing status flip-flop relay which allows me to use the green button switch for both start and pause. T01 is the main retentive timer, set to 16 minutes (960 seconds). T02 and T03 are the timers used for slow and fast blinking, respectively. G01 is a compare operation, which on the Teco SG2 is an output (it is often an input on PLC’s), so it required its own line on the ladder diagram. It is used to ensure that the timer (T01) is timing before the blinking pause output will be enabled.
You will see that G01 has a V after the numbers in the block off to the side of the coil. The compare function on the Teco SG2 is primarily for comparing analog voltages, but it can be used to compare any two numbers. In this case, it is comparing the accumulated time in T01 against “0″ to ensure that the timer is some number greater than 0 and has therefore begun timing. This way if the timer has not started timing, the indicator light will not be blinking.
Click to Enlarge.
The indicator light also makes a great night light.
Here is a zip file containing the ladder logic diagram: Feeding Timer. You can download the SG2 programming software, load the ladder logic program, and start the emulator to see how it works. You can change it and play with it all you like.
