Experimental Physics and Industrial Control System
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Ryan,
I'm looking to find something that works out of the box. The PT100 is a
requirements.
Beckhoff has a KL320X, I thought someone has experienced on that...
I've to balance the cost and the reliability of this solution.
Thansk,
-Mauro
On 1/12/2016 5:16 PM, Ryan Pierce wrote:
Does "cost effective solution" apply to parts only or include labor?
Are you willing to build your own solution, or are you looking for
something that works out of the box? If the former:
I've worked with voltage-based analog temperature sensors (TMP36)
before. In that case, I designed a Raspberry Pi shield board that
included an 8-channel 10-bit ADC addressable via SPI. See
http://www.mackenziegems.com/2013/03/14/chillmon-board/ I imagine you
could do the same thing with resistance-based PT100's if you set up a
voltage divider for each input. The board fabrication and component
price was $22 for 8 channels, although you'd need to add in a
Raspberry Pi, SD card, power supply, etc. For your application, I
might consider dispensing with the Pi altogether, making a shield
board for an AVR microcontroller, and have that communicate the
channel data with an IOC via USB or TTL serial. I'm amazed at how
small, inexpensive, and powerful these AVRs have become, in particular
the Teensy: https://www.pjrc.com/teensy/
Does it have to be PT100? I strongly prefer digital sensors if
possible. I'm currently using DS18B20 OneWire temperature sensors for
my brewing project. They are individually addressable and can be
strung together in a bus. Resolution is 1/16 degree C if you're
willing to wait 750 ms for a conversion; you can configure them to use
lower precision which will reduce the conversion time. I don't know
how far these 100 sensors are spaced out; you may run into bus length
limitations with OneWire, but I've seen documents that talk about
improving OneWire performance for long or noisy buses. I'm using an
AVR microcontroller to bit bang the OneWire bus, and this is queried
via USB serial. OneWire has the ability to detect a broken bus, a
non-reporting device, or a transmission error via a CRC. The AVR can
check this and raise an EPICS alarm if the output becomes invalid. You
could also use one microcontroller to run several independent OneWire
buses. This approach is likewise very inexpensive.
Ryan
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Mauro Giacchini
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INFN Laboratori Nazionali di Legnaro
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Tel. +39 049 8068 558
Fax 558
EPICS _at_ LNL http://www.lnl.infn.it/~epics/
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scratch in ITALY is in production since begin 2010!!
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