Omega Vehicle Security OM5-C manual OM5-IP4/IC4/IN4 Linearized 4-Wire RTD Input Modules

OM5-IP4/IC4/IN4 Linearized 4-Wire RTD Input Modules

FEATURES

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

●TRUE 4-WIRE INPUT

●LINEARIZES RTD SIGNAL

●HIGH LEVEL VOLTAGE OUTPUT

●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

In RTD temperature measurement applications requiring a very high level of accuracy, the OM5 4-Wire RTD input module offers a significant advantage over 3-wire measurement techniques (Figure 1). The OM5 measures only the voltage dropped across the RTD and almost completely ignores the resistance or length of the RTD lead wires. The OM5 3-Wire RTD module provides lead resistance compensation, but requires equal lead resistances, while the 4-wire modules do not require matched lead resistances.

Each OM5 4-wire 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. 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 a precision current source. The excitation current is available on two leads which are separate from the two input signal measuring leads. The excitation current does not flow in the input signal leads, which allows RTD measurement to be totally independent of lead resistance. The excitation current is very small (0.25mA for 100 Ω Pt and 120 Ω Ni and 1.0 mA 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 provides protection against accidental connection of power-line voltages up to 240VAC.

+EXC

4

LPF

Linearizer

Isochopper™

20

VOUT

	+In
RTD
4 Wire	–In
RTD
	–EXC

4

3

2

1

6

5

3

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

NC–V

2

NC

+V

–V

Isolated

Field-Side

Power

Power

Oscillator

17

+5V

16

Power Common

FIGURE 1. OM5-IP4/IC4/IN4 Block Diagram.

12