National Instruments FIeldPoint FP-AO-200 Operating Manual

FP-AO-200

8 Channel, 20 mA Loop Output Module

Highlights

• Eight 0-20/4-20 mA outputs

• 0.5 mA over-range ability

• 12-bit resolution DACs

• Open current loop indicators

• 3,000 V input-to-output isolation

• Double insulated for 250 V safe working voltage

• Up to 1 kOhm load impedance (with 24 V loop supply)

• Short circuit protection

• -40° to +70° C operation

Overview

The FP-AO-200 is a FieldPoint analog output module with eight
0-20/4-20 mA current loop outputs. You can use the FP-AO-200 to
drive devices using process current loops of either the 0-20 mA or
4-20 mA standards. Hot plug and play operation, safety isolation,
onboard diagnostics such as open loop detection, and over-ranging
ability ensure that installation and maintenance are as trouble free
as possible.

These operating instructions describe the installation, features, and
characteristics of the FP-AO-200. For details on configuring and
accessing the FP-AO-200 over a network, refer to the user manual
for the particular FieldPoint network module you are using with the
FP-AO-200.

FieldPoint ™ is a trademark of National Instruments Corporation. Product and company names are
trademarks or trade names of their respective companies.

321634A-01

©

Copyright 1997 National Instruments Corp. All rights reserved. July 1997

Module Installation

The FP-AO-200 mounts on a FieldPoint terminal base (FP-TB-xx)
unit. The hot plug and play operation of the FP-AO-200 allows you
to install it onto a powered terminal base without disturbing the
operation of other modules or terminal bases. The FP-AO-200
receives operating power from the terminal base. Current loop
power is externally supplied.

To install the FP-AO-200, refer to Figure 1 and follow these steps:

1. Slide the terminal base key to either position X (used for any
module) or position 2 (used for the FP-AO-200 module).

2. Align the FP-AO-200 alignment slots with the guide rails on
the terminal base.

3. Press firmly to seat the FP-AO-200 in the terminal base. The
terminal base latch locks the FP-AO-200 into place when it is
firmly seated.

4. Connect a current loop supply for the outputs to the V and C
terminals of the terminal base.

Key

Latch

Alignment

Slot

Guide Rails

Terminal BaseI/O Module

Figure 1.

Module Installation Diagram

Field Wiring

The FP-AO-200 sources current from an external loop supply to a
load (or field device). The terminal base provides connections for
both the external loop supply and for the eight output channels.
Figures 2a and 2b show examples of these basic wiring
connections. The positive terminal of the loop supply is connected
to the V terminal; the negative (or common) terminal is connected
to the C terminal. Each channel has an output terminal, I
common terminal, COM (internally connected to the C terminal);

2

out

; a

and a supply terminal, V
terminal). As the figures show, connections to the C and COM

(internally connected to the V

sup

terminals are not required but may be used to simplify wiring. You
may use connections to the V
V terminal to devices which require supplementary power.

VC

I

out

terminals to route power from the

sup

Loop

Supply

V

I

out

Loop

Supply

Load

COM

I

out

Load

COM

a. With COM Connection b. Without COM Connection

I

out

Load

Load

Figure 2. Basic Field Connections (Two channels shown)

Table 1 lists the terminal assignments for the signals associated
with each channel.

Table 1. Terminal Assignments

Terminal Numbers

Channel

I

out

0 1 2, 18 17
1 3 4, 20 19
2 5 6, 22 21
3 7 8, 24 23
4 9 10, 26 25
5 11 12, 28 27
6 13 14, 30 29
7 15 16, 32 31

COM V

sup

3

Current Output Circuit

The output circuit of the FP-AO-200 is a sourcing current output,
which means that it is designed to source current provided by an
external loop supply to a device or load capable of sinking this
current to the common voltage of the loop supply. The FP-AO-200
can operate with an external loop supply from 5 to 24 VDC;
however, this voltage dictates the maximum load impedance which
the FP-AO-200 can drive. With a 24 VDC loop supply, each output
can drive up to 1 kOhm of load impedance. With a 5 VDC loop
supply, each output can only drive up to 100 Ohms. The
FP-AO-200 detects and reports error conditions due to excessive
loads or insufficient loop supplies. For more information, refer to
the Open Loop Detection section in this document.

The FP-AO-200 updates the output channels as new values are sent
to it by the network module. The time it takes to respond to a
change on a single channel is between 3 and 6 ms. The response
time to changes on all eight channels is 24 to 27 ms.

Figure 3 shows a diagram of the current output circuit of a single
channel.

V

V

sup

Open Loop

Indicator

12-Bit

Isolated DAC

Current

Sense

C

I

out

COM
COM

Figure 3.

FA-A0-200 Current Output Circuit

The FP-AO-200 has several unique features that promote reliable
operation, ease of use, and solid performance. These features are
described below.

4