LumaSense Technologies M67 - Manual (Page 27)

M67, M67S Manual
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8. Wiring
8.1 Wiring the M67/M67S
The INFRADUCER requires a D.C. power supply that provides a minimum of 18 volts, and a maximum of 40 volts. The
supply voltage is dependent on the circuit resistance. See Table 2 for required voltages. DO NOT EXCEED 40 VDC across
the terminals of the INFRADUCER. shows the connections. They are plus (+), minus (-) and ground as marked on the rear
panel. When the cooling jacket is used, remove the rear cap to expose the INFRADUCER. For best results, use twisted pair,
shielded cable. DO NOT RUN CABLE IN CONDUITS THAT CONTAIN A.C. POWER LINES since this could induce
unwanted noise signals in the current loop. See Figure 20 and Figure 21 for typical loop wiring.
A typical loop wiring diagram is shown in Figure 20. Locate the D.C. power supply behind (or inside) your system control
panel (or cabinet). Mount the receiver, indicator, controller, recorder, etc. on your control panel or cabinet. The two-wire cable
connects these items in series as shown in the diagram. If the plus (+) and the minus (-) on the INFRADUCER connections are
reversed, no signal will flow. (No damage will occur).
All 4-20 mA receiver instruments have input resistance specified in their instructions. Resistance can be typically from 1 to
1000 ohms. When using the INFRADUCER to drive more than one receiver, the sum of the resistances will be the total loop
resistance. When a very long cable is used, the total resistance of the wire in both directions must be added. (The minimum
supply voltage that can be used depends on the total loop resistance). When specifying the D.C. power supply to be used in
your system, refer to the table below to find the minimum requirements.
DC Supply Volts 18 19 20 21 22 23 24 25 26 27 28 29
Max. Resistance Ohms 100 150 200 250 300 350 400 450 500 550 600 650
DC Supply Volts 30 31 32 33 34 35 36 37 38 39 40
Max. Resistance Ohms 700 750 800 850 900 950 1000 1050 1100 1150 1200
Table 2 - Maximum circuit resistance for infraducer power supply
Example: The INFRADUCER is to drive a recorder and digital indicator.
The recorder input impedance is 250 ohms.
The digital indicator impedance is 100 ohms.
The resistance of the line is 2 ohms (each conductor).
Total loop resistance equals 354 ohms.
(Note: In D.C. circuits, resistance and impedance are synonymous).
Using the table, look up the next higher value (max. ohms is 400). You need a D.C. supply of at least 22 volts for a reliable
system; a 24 volts standard supply is sufficient. If you plan to add receiver instruments in the future, specify a higher supply
voltage. If you plan to add more INFRADUCERS, specify a supply capable of delivering approximately 22 mA times the
number of units planned. Some receiver instrument specify the loop voltage drop instead of input resistance. In this case, add
this figure to minimum supply voltage found using the Table above.
Example: The recorder input is 250 ohms.
The digital indicator has a 5.6 volts drop in the loop.
The line resistance is again 4 ohms total.
Total loop resistance now is 254 ohms.
Look up 300 ohms in the Table above to find that the supply must be 20 volts minimum. Add the
digital indicator's voltage drop.
20 volts + 5.6 volts = 25.6 volts D.C.
The power supply has to be at least 25.6 volts for the loop to operate. You can select, for example,
any supply from 26 to 40 volts D.C.