Experimental Physics and
Industrial Control System

Jack <[email protected]> · Wed, 13 Jan 2016 08:25:37 +0100

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

--
________________________________________________________________________

Mauro Giacchini

Control Systems Specialist
INFN Laboratori Nazionali di Legnaro
Viale Università 2
I 35020 Legnaro (Padova)
Tel. +39 049 8068 558
Fax               558

EPICS _at_ LNL http://www.lnl.infn.it/~epics/

...the first EPICS installation to the project SPES realized from the
scratch in ITALY is in production since begin 2010!!
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System