Omega Vehicle Security OM5-C OM5-IP/IC/IN, Linearized 2- or 3-WireRTD Input Modules, Features

OM5-IP/IC/IN

Linearized 2- or 3-Wire RTD Input Modules

FEATURES

●INTERFACES TO 100Ω PLATINUM, 10Ω COPPER, OR 120Ω NICKEL RTDs

●LINEARIZES RTD SIGNAL

●HIGH LEVEL VOLTAGE OUTPUTS

●1500Vrms TRANSFORMER ISOLATION

●ANSI/IEEE C37.90.1-1989 TRANSIENT PROTECTION

●INPUT PROTECTED TO 240VAC CONTINUOUS

●160dB CMR

●95dB NMR AT 60Hz, 90dB AT 50Hz

●CSA CERTIFIED, FM APPROVED, CE COMPLIANT

●MIX AND MATCH OM5 TYPES ON BACKPANEL

DESCRIPTION

Each OM5 RTD input module provides a single channel of RTD input which is filtered, isolated, amplified, linearized, and converted to a high level analog voltage output (Figure 1). This voltage output is logic switch controlled, which allows these modules to share a common analog bus without the requirement of external multiplexers.

The OM5 modules are designed with a completely isolated computer side

circuit which can be floated to ±50V from Power Common, pin 16. This complete isolation means that no connection is required between I/O Common and Power Common for proper operation of the output switch. If desired, the output switch can be turned on continuously by simply connecting pin 22, the Read-Enable pin to I/O Common, pin 19.

RTD excitation is provided from the module by two matched current sources. When using a three-wire RTD, this method allows an equal current to flow in each RTD lead, which cancels the effects of lead resistances. The excitation currents are very small (0.25mA for 100Ω Pt and 120Ω Ni, and 1.0mA for 10Ω Cu) which minimizes self-heating of the RTD.

Signal filtering is accomplished with a six-pole filter which provides 95dB of normal-mode-rejection at 60Hz and 90dB at 50Hz. Two poles of this filter are on the field side of the isolation barrier, and the other four are on the computer side. After the initial field-side filtering, the input signal is chopped by a proprietary chopper circuit. Isolation is provided by trans- former coupling, again using a proprietary technique to suppress transmis- sion of common mode spikes or surges. The module is powered from +5VDC, ±5%.

A special input circuit on the OM5 modules provides protection against accidental connection of power-line voltages up to 240VAC.

3 and 4 Wire(1)

2 Wire

+EXC

4

		Linearizer
LPF	Isochopper™

20

VOUT

	4
+In
RTD	3
–In	2
–EXC	1
4 Wire(1)

6

5

3 NC

Surge

Suppression

and

Protection

Amplifier				LPF
Pat Pending
	+V		–V
		Isolated
	Computer-Side
		Power

19

22

I/O Common

RD EN\

Backpanel

Term Block

1		–V
NC
2
	+V
NOTE: (1) 4-wire sensors may be	–V
used with this module. However,
for true 4-wire measurement,
use OM5-IP4/IC4/IN4.

–V
Isolated	Power
Field-Side
	Oscillator
Power

17

+5V

16

Power Common

FIGURE 1. OM5-IP/IC/IN Block Diagram.

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