A temperature control system consist of four thermostats controlling three heati

Question

A temperature control system consist of four thermostats controlling three heating units. The thermostat contacts are set to close at 50, 60, 70 and 80 degrees Fahrenheit, respectively. The PLC ladder logic program is to designed so that a temperature below 50 degree F, three heaters are be to be on. Between 50 60 60 degree F two heater are to be on. For 60 to 70 degree F, one heater is to be on. Above 80 degree F, there is a safety shutoff for all three heaters in case one stays on because of malfunction. A master switch is to be used to turn the system on and off. Prepare a typical PLC program for this control process.

Explanation / Answer

NOW my little contribution to understanding the basics...PLC's were created to replace RELAY logic. Relays were electrical devices that were turned on or off depending on conditions (ie inputs). A standard relay logic schematic: Stop PB Start PB __|__ 1-------0__|__0-------0 0------------------(relay1)----2 | | |---| |--| relay1 auxillary contact . Note: Number 1 is power and Number 2 is common connection for power..ok? Lets assume conventional flow for power..ie from positive (1) to negative (2) in this case. Stop is a normally closed pushbutton so power flows thru it to the Start pushbutton(a normally OPEN pushbutton) and one side of Relay 1 auxillary contact. When you PUSH on the Start PB then power flows to the relay which closes/energizes it...which in turn "latches/holds" relay1 closed via the auxillary contacts. With a PLC things are a little different because they offer versatility but for the basics they follow the same format. -----|input1|--------------------(relay1) | | |--|relay1|-| . In this case all you need is power on or off from an input, depending on if you use XIO or XIC to turn on and latch the relay. Its all done in software. Others will offer more and better assistance but hopefully this will assist you in the basics. Post more if you need more. NOTE: I noticed the fix isnt in on problem with text going off screen after posting ladder..ie still have to add extra character.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.