Multilin SR469, Инструкция по эксплуатации

Страница: 26 / 270

ELECTRICAL 2. INSTALLATION
2-12
2.2.8 ANALOG INPUTS
Terminals are provided on the SR469 for the input of four 0-1mA, 0-
20mA, or 4-20mA current signals (field programmable). This current
signal can be used to monitor any external quantity such as:
vibration, pressure, flow, etc. The four inputs share one common
return. Polarity of these inputs must be observed for proper
operation The analog input circuitry is isolated as a group with the
Analog Output circuitry and the RTD circuitry. Only one ground
reference should be used for the three circuits. Transorbs limit this
isolation to
±
36 volts with respect to the SR469 safety ground.
In addition, the +24Vdc analog input supply is brought out for con-
trol power of loop powered transducers (see Figure 2-20). Refer to
the Specifications section of this manual for maximum current
draw from this supply.
Figure 2-20 LOOP POWERED TRANSDUCER CONNECTION
2.2.9 ANALOG OUTPUTS
The SR469 provides 4 analog output channels, which when ordering are selected to provide a full-scale range of either 0-1 mA (into a
maximum 10 k
Ω
impedance), or 4-20 mA (into a maximum 1200
Ω
impedance). Each channel can be configured to provide full-scale output
sensitivity for any range of any measured parameter.
As shown in the wiring diagram of Figure 2-12, these outputs share one common return. Polarity of these outputs must be observed for
proper operation. Shielded cable should be used, with only one end of the shield grounded, to minimize noise effects.
The analog output circuitry is isolated as a group with the Analog Input circuitry and the RTD circuitry. Only one ground reference should be
used for the three circuits. Transorbs limit this isolation to
±
36 volts with respect to the SR469 safety ground.
If a voltage output is required, a burden resistor must be connected at the input of the SCADA measuring device. Ignoring the input
impedance of the input, R
LOAD
= V
FULL SCALE
/ I
MAX
. For 0-1 mA, for example, if 5 V full scale is required to correspond to 1 mA, R
LOAD
= 5 / 0.001 =
5000 ohms. For 4-20 mA, this resistor would be R
LOAD
= 5 V / 0.020 = 250 ohms.