Want To Force 4-20mA With 12V Battery

Turn your caps lock off and tell me what a DCS is please?

John.

DCS is Distributed Control System. Some are made by Foxboro and Fisher Controls. I think Honeywell and Rosemount make these also.

Ref: Communications & Electronics Section

http://cr4.globalspec.com/thread/15399/LCD-Screen-Ugly-When-Off

Answer #24

hi friend the transmitter will operate on 10 to 27 vdc but the cable resistance may play an important role in the transmission of the milli amps from the transmitter so the milli amps can be transmitted but the thickness of the wire strands and cross sectional area and the resistance value of the cable overall length decides the receiving end voltage due to the voltage drop due to the resistance it will reduce the milliamps transmission also

first u find out the different thickness of copper wire resistance value and calculate the total length of the resistance and calculate the voltage drop by using the formula

(V) drop = Current (I) * Resistance(R)

V = I * R

http://celesco.com/faq/420.htm

Is it a 2-wire instrument? If so, then provided the overall loop resistance is lower than the limit imposed by the supply voltage AS STATED IN THE ORIGINAL EQUIPMENT MANUFACTURER'S MANUAL, then there isn't a problem. The whole idea of milliamp transmission is that the effect of cable resistance can be ignored.

The circuit?

• Supply +24VDC fuse to the transmitter +terminal down one of the 2 cores in the cable
• transmitter -terminal to the control system analogue input +terminal down the other of the cores in the cable
• analogue input -terminal to the supply 0VDC terminal within the panel.

Job done.

Please clear your statment .You have 24 V dC from DCS and needs 12 V. If Distace is long put the repeater.

Not sure about the whole set-up; It seems to me that what he wants is to boost the signal somewhat. I believe he can obtain this by using the DC source as, pointed out by others, from the DCS. Followng established procedures, not a battery!

I do not see why you would need the 12V battery.

If your DCS has 4 to 20mA inputs, just directly connect your transmitter to it using the built-in 24Vdc to power the loop.

I'm assuming that the 24Vdc is for powering instruments.

If I were in your place, the DCS user manual should have the information you're looking for. Your question does not give a clear enough picture for me to give you a clear answer.