Voltage Available - Fisher FIELDVUE DVC6200 Instruction Manual

Instruction Manual
D103409X012
Figure 2‐27. HART Filter Application
NON‐HART BASED DCS
I/O
Tx Tx
A6188‐1

Voltage Available

The voltage available at the DVC6200 digital valve controller must be at least 11 volts DC. The voltage available at the
instrument is not the actual voltage measured at the instrument when the instrument is connected. The voltage
measured at the instrument is limited by the instrument and is typically less than the voltage available.
As shown in figure 2‐28, the voltage available at the instrument depends upon:
D the control system compliance voltage
D if a filter, wireless THUM adapter, or intrinsic safety barrier is used, and
D the wire type and length.
The control system compliance voltage is the maximum voltage at the control system output terminals at which the
control system can produce maximum loop current.
The voltage available at the instrument may be calculated from the following equation:
Voltage Available = [Control System Compliance Voltage (at maximum current)] - [filter voltage drop (if a HART filter is
used)] - [total cable resistance  maximum current] - [barrier resistance x maximum current].
The calculated voltage available should be greater than or equal to 11 volts DC.
Table 2‐2 lists the resistance of some typical cables.
The following example shows how to calculate the voltage available for a Honeywellt TDC2000 control system with a
HF340 HART filter, and 1000 feet of Belden
Voltage available = [18.5 volts (at 21.05 mA)] - [2.3 volts] - [48 ohms  0.02105 amps]
Voltage available = [18.5] - [2.3] - [1.01]
Voltage available = 15.19 volts
I/O
HART
FILTER
4‐20 mA + HART
DIGITAL VALVE
CONTROLLER
VALVE
t
9501 cable:
Installation
May 2013
35