Controls Tricks of the Trade

[joey791]

Hey everyone, how bout we start a thread to help out new people and old, anything from straight and simple to generic.


I saw someone post this already but

on a 4 to 20ma device you can use a 250 ohm resistor to make the device 0 to 5 VDC or 500 ohm for 0 to 10 VDC

Honeywell Modutrol Motors-Have a bunch of them that are potentiometer and you need a DC input instead? Honeywell makes a module that you can plug into the motor to change it to VDC, you can find the PDF on the module here
http://hbctechlit.honeywell.com/tech...0s/63-2235.pdf

Also Honeywell has the famous "Gray Book" you can find it here, its a big download
http://68.209.216.66/html/Training/H...llTraining.htm

[control_noob]

Thanks for the links, good stuff.

[wellhung]

your grey book link is dead.

[sysint]

This should just be a standard posting at the top of this section:

HONEYWELL ENGINEERING MANUAL of AUTOMATIC CONTROL for COMMERCIAL BUILDINGS

....Otherwise known as the Honeywell Grey Manual.

[codewriter]

http://www.kele.com/webservices/inde...h/trindex.html

[ctrlguy]

on a 4 to 20ma device you can use a 250 ohm resistor to make the device 0 to 5 VDC or 500 ohm for 0 to 10 VDC

Just a slight correction: 250 ohms gets you 1-5VDC. 500 ohms gets you 2-10VDC. Good ole Ohm's Law: 500*.004=2 500*.02=10

[joey791]

Just a slight correction: 250 ohms gets you 1-5VDC. 500 ohms gets you 2-10VDC. Good ole Ohm's Law: 500*.004=2 500*.02=10

It was 2 years ago, you can give me a break on the math

Also the Honeywell book in book form

http://store.hydronicpros.com/product.php?qcp=1028

[incontrol]

Why'd ya leave out the 1000ohm? That converts ma to volts directly. I've used AOs as constant DC sources before.

[wellhung]

in control, please explain about the 1000 Ohm set-up.

[codewriter]

1000ohm will turn 0-20ma to 0-20vdc
500ohm will turn 0-20ma to 0-10vdc
375ohm will turn 0-20ma to 0-7.5vdc
250ohm will turn 0-20ma to 0-5vdc
etc....
Use the formula (V = I x R)

Some controllers have a max load of 500ohms, etc... So you cant do this with everything.


Edit: almost forgot about this site -
http://www.csgnetwork.com/ohmslaw.html

Use the "To calculate the circuit voltage" (V = I x R)

So on the webpage, in the Amps field put .004 (4ma), put 500 in the Ohms field, click calculate and you get 2 volts,
etc...

[wellhung]

basic question------------what is the difference between a transmitter and a transducer?

[twisted pair]

A Transmitter would be a Field Device connected to a DDC Controller as an Analog Input Point, such as a static pressure transmitter or %RH.

A Transducer is connected to a DDC Controller on a Analog Output Point, which would modulate a signal to a Field Device. 0-10 vdc, 4-20 mA, 0-20 PSI, 0-135 ohms etc...

[codewriter]

They are all transducers in my mind. A transducer is an electronic device that converts "energy" from one form to another.

When it comes to pnuematics, I use the term transmitter though, it was just how I learned it back in the day.

I think a lot of people interchange this word, and most people will probably know what your talking about even if you do not use it so called "properly".