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Manual Documentation Number: RT-12 series-4006m 27
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
Typical Application: 4-20 mA to Voltage Conversion
This section will describe how a typical system is converted from a 4-20mA or 0-
20mA current signal to a 1-5Vdc or 0-5Vdc voltage signal.
The RT series RTU’s do not allow for a direct 4-20mA connection. A simple 250
Ohm, 1%, ¼ Watt, resistor from the input of the respective terminal to ground will
convert the current signal to a voltage signal. If a 250 Ohm resistor is not available a
249 Ohm, 1%, ¼ Watt, resistor will work.
The same example is true for a 0-20mA current signal. The only exception is the
voltage will swing from 0-5Vdc. If a current source is applied to a respective input
without a resistor the data will not be correct and a signal error will occur.
The example below shows analog Input 1 converted from 4-20 to 1-5Vdc. Keep in
mind, if an RTU is used in Peer to Peer mode, the receiving device will output a 1-
5Vdc voltage on the respective output.
28 Manual Documentation Number: RT-12 series-4006m
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
Configuration Cable Description
Serial cable used in configuration and connectivity of B&B Electronics’ RT-series
controllers.
Pin# Connection (color) Description
DB9-Pin#2 Green TX
DB9-Pin#3 Red RX
DB9-Pin#5 Yellow GND
DB9-Pin#7 Black CTS
-Use a straight-through, common, Category 5 cable (available from B&B Electronics) for
connection to the RT-series RTU’s.