2 internal features of the isa – m, Figure 2: internal features of the isa – m – ENMET ISA-M User Manual

Page 5

ISA – M

ENMET Corporation

2.2 Internal Features of the ISA – M

Figure 2 shows the circuit board and terminal blocks housed inside the hinged oiltight control unit. Specific relays and
adjustments are defined in the table below.

Feature

Description

Internal Relay Contacts

There is one relay for each alarm level. Relays can be used to activate an external remote
alarm signal when a hazardous gas level is detected, or when the ac or dc power is
interrupted. These are double-pole relays with terminals "normally open", "normally
closed" and "common" (see figure 3 for relay contact hook-up).

Potentiometers(POT)

The unit has five potentiometers. These vary circuit resistances and are essential to
calibration procedures. These potentiometers are described below.

Heater Adjust
(RV32)

For adjusting the sensor heater voltage (see section 4.4)

Low Level Alarm
(RV35)

For low-level alarm adjustment (calibration, see section 6.2).

High Level Alarm
(RV34)

For high-level alarm adjustment (calibration, see section 6.2).

Meter Adjust
(RV33)

To adjust and set the meter for appropriate gas response during calibration. (See section 6.2)

Purge Adjust
(RV38)

For adjusting the sensor heater voltage on units that require periodic purging (cleaning) of
the sensor. (See section 4.4)

Figure 2: Internal Features of the ISA – M

Non-Latching Relay contacts:
Identified below is the non-powered
(power to unit is off), alarm positions of
the non-latching relay contacts.

Terminal Block 2 see Figure 5
Relay 1

High Alarm

Relay 2

Low Alarm

OTE

N.C.= normally closed
N.O.= normally open

Suggested wiring configuration for Utilizing Relay Contacts
(manual on/off switch is suggested; user supplied component)

Common
Contact

Horn

Normally
Closed
Contact

Manual On/Off

Switch

Black

White

110 Vac

Power supply Outside

of Control Unit

Heater Adjust
(POT RV32)

High-level Alarm
(POT RV34)

Meter Adjust
(POT RV33)

Low-level Alarm

(POT RV35)

110/115

220/230*
*See section 4.2

12 V

Input

Internal Relay

Contacts

Purge Adjust
(POT RV38)