Jinx wrote:
> I'm assessing a job, which I think a low-end 18F can do fairly simply. The
> logic is quite straight-forward. Inputs are two 4-20mA transducers, a mains
> relay, and two temperature sensors, with a real-time clock. Outputs are
> a couple of alarm lines, LCD, and a few pushbuttons to set parameters
>
> The scenario might be something like - If transducer1 is a certain value
> and temperature sensor2 is a certain value, then turn on the mains and
> measure temperature sensor1 after 1 minute to make sure the appliance
> (a chiller) is running. And various IF....THEN combos like that
>
> I was talking over the pricing structure with a couple of people and they
> both suggested that I base it at less than the cost of an 'industrial PLC'
> which would be needed. Their thought is that the lower (but not too low)
> price mentioned in the same breath as a PLC will make my PIC sound
> more attractive. Can't say I'm 100% about that but they won't shut up
> about PLCs !
>
> I'm a complete ignoramus in the PLC department
>
> http://en.wikipedia.org/wiki/Programmable_logic_controller
>
> To me, after reading that, it seems a PLC is way OTT for this job, and
> especially if you know how to program a micro yourself. This assessment
> may be for 300 units (optimistic "Everyone will want one" salesman !!)
>
> I guess the material costs, not including sensors, using a PIC may be around
> NZ$70 (US$35-$40), and software perhaps a little less (@ Q = 300), then
> there's markup on that
>
> Can anyone with practical experience of PLCs give me any advice as to
> whether the cost of a PLC system is even worth considering ? And, if so,
> how do prices compare ?
>
> TIA
>
>   
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>   
Hi Jinx,

Zelio - Schneider have a range of so called smart relays
http://www.schneider-electric.com/corporate/en/products-services/automation-control/products-offer/range-presentation.page?p_function_id=18&p_family_id=233&p_range_id=531

They provide a free down load of there ladder logic.
http://www.schneider-electric.com/corporate/en/products-services/automation-control/products-offer/range-presentation.page?p_function_id=18&p_family_id=233&p_range_id=531#

Regards Roy

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