Fisher FIELDVUE DVC6200 Instruction Manual page 36

Installation
May 2013
Figure 2‐28. Determining Voltage Available at the Instrument
COMPLIANCE VOLTAGE
CONTROL
SYSTEM
+
HART FILTER
-
(if used)
Calculate Voltage Available at the Instrument as follows:
Control system compliance voltage
– Filter voltage drop (if used)
– Intrinsic safety barrier resistance (if used) x maximum loop current
– Smart Wireless THUM adapter voltage drop (if used)
– Total loop cable resistance x maximum loop current
= Voltage available at the instrument
NOTES:
Obtain filter voltage drop. The measured drop will be different than this value. The measured filter voltage drop
1
depends upon control system output voltage, the intrinsic safety barrier (if used), and the instrument. See note 3.
The voltage drop of the THUM adapter is linear from 2.25 volts at 3.5 mA to 1.2 volts at 25 mA.
2
The voltage available at the instrument is not the voltage measured at the instrument terminals. Once the instrument is
3
connected, the instrument limits the measured voltage to approximately 9.0 to 10.5 volts.
Table 2‐2. Cable Characteristics
Cable Type
BS5308/1, 0.5 sq mm
BS5308/1, 1.0 sq mm
BS5308/1, 1.5 sq mm
BS5308/2, 0.5 sq mm
BS5308/2, 0.75 sq mm
BS5308/2, 1.5 sq mm
BELDEN 8303, 22 awg
BELDEN 8441, 22 awg
BELDEN 8767, 22 awg
BELDEN 8777, 22 awg
BELDEN 9501, 24 awg
BELDEN 9680, 24 awg
BELDEN 9729, 24 awg
BELDEN 9773, 18 awg
BELDEN 9829, 24 awg
BELDEN 9873, 20 awg
1. The capacitance values represent capacitance from one conductor to all other conductors and shield. This is the appropriate value to use in the cable length calculations.
2. The resistance values include both wires of the twisted pair.
36
TOTAL LOOP
CABLE RESISTANCE
INTRINSIC SAFETY
BARRIER
(if used)
1
3
(1)
Capacitance Capacitance
pF/Ft
61.0
61.0
61.0
121.9
121.9
121.9
63.0
83.2
76.8
54.9
50.0
27.5
22.1
54.9
27.1
54.9
THUM ADAPTER
(IF USED)
R
Example Calculation
18.5 volts (at 21.05 mA)
– 2.3 volts (for HF300 filter)
– 2.55 volts (121 ohms x 0.02105 amps)
2
– 1.01 volts (48 ohms x 0.02105 amps for
1000 feet of Belden 9501 cable)
= 15.19 volts, available—if safety barrier (2.55 volts)
is not used
(1)
Resistance
pF/m Ohms/ft
200
200
200
400
400
400
206.7
273
252
180
164
90.2
72.5
180
88.9
180
Instruction Manual
VOLTAGE
+
AVAILABLE AT THE
INSTRUMENT
-
(2)
Resistance
Ohms/m
0.022 0.074
0.012 0.037
0.008 0.025
0.022 0.074
0.016 0.053
0.008 0.025
0.030 0.098
0.030 0.098
0.030 0.098
0.030 0.098
0.048 0.157
0.048 0.157
0.048 0.157
0.012 0.042
0.048 0.157
0.020 0.069
D103409X012
(2)