Installation RLead ++
Instrument No. 1
+
− RLead
Instrument No. 2
Readout Device No. 1
+ Battery Backup
−
dc Power Supply −
+ RLead
3
− RLead
Readout Device No. 2 Between 230 and 1100 if no Load Resistor
E0364 / IL
To Additional Instruments
Figure 3-13. Multichannel Installations
attach the device to the loop + and − terminals inside the terminal box to provide local communications with the instrument.
Test Connections WARNING Personal injury or property damage caused by fire or explosion may occur if the following procedure is attempted in an area which contains a potentially explosive atmosphere or has been classified as hazardous. Confirm that area classification and atmosphere conditions permit the safe removal of the terminal box cap before proceeding. Test connections inside the terminal box can be used to measure loop current across an internal 1 ohm resistor. 1. Remove the terminal box cap. 2. Adjust the test meter to measure a range of 0.001 to 0.1 volts. 3. Connect the positive lead of the test meter to the + connection and the negative lead to the T connection inside the terminal box. 4. Measure Loop current as: February 2007
Voltage (on test meter) 1000 = milliamps example: Test meter Voltage X 1000 = Loop Milliamps 0.004 X1000 = 4.0 milliamperes 0.020 X 1000 = 20.0 milliamperes 5. Remove test leads and replace the terminal box cover.
Multichannel Installations You can connect several instruments to a single master power supply as shown in figure 3-13. In this case, the system may be grounded only at the negative power supply terminal. In multichannel installations where several instruments depend on one power supply, and the loss of all instruments would cause operational problems, consider an uninterruptible power supply or a back-up battery. The diodes shown in figure 3-13 prevent unwanted charging or discharging of the back-up battery. If several loops are connected in parallel, make sure the net loop impedance does not reach levels that would prevent communication. Note that to provide a 4−20 mA analog output signal, the DLC3010 must use HART polling address 0. Therefore, if a multichannel installation is used with all transmitters in 4−20 mA output mode, some means must be provided to isolate an individual transmitter for configuration or diagnostic purposes. A multichannel installation is most useful if the instruments are also in multi-drop mode and all signaling is done by digital polling.
3-13