Sierra Monitor Corporation 5000 Toxic Gas Transmitter Component Locator, Service, Page

SMC sierra monitor corporation Sentry Instruction Manual - Version 6

The SENSOR FAILURE message for toxic gas sensors does not indicate a specific failure of the sensor but indicates that the sensor is not correctly connected to the electronics. If this message appears check that the sensor harness is correctly installed to the connector on the bottom electronics board.

The gas sensor which is located inside the sensor assembly housing can be replaced without replacement of the housing. To replace the sensor:

1.Confirm that system power has been removed.

2.Remove the transmitter electronics board from the main housing and unplug the sensor harness from the transmitter electronics.

3.Unscrew the sensor housing from the bottom of the enclosure

4.Hold the sensor assembly so that the harness faces down and the sensor faces up. Unscrew and remove the round section of the housing from the hex

section. Be careful not to lose the spacer

Figure 7-12

washer which will be sitting on top of the

Toxic Gas Transmitter Component Locator

exposed sensor.

5.

Carefully pull the old sensor straight up from the

1.

Adjust

the

span

potentiometer so

that

it

is

approximately

mid

range.

(Twenty

turns

socket.

clockwise and tens turns counter-clockwise).

6.

Orient the

new sensor

so that

the

sensor pin

2.

Remove system

power and remove

both

the

labeled “C” faces the socket labeled “C” which is

transmitter

and

the sensor assembly

from

the

on the far side of the board from the vertical reed

enclosure. Remove the sensor assembly cover so

switch. The reed switch will slide into a hole on

that the sensor is visible.

the side of the new sensor. Press the new

3.

Plug the sensor harness into

the

transmitter

sensor’s pins into the three sockets.

7.

Carefully

replace the

cover

on

the sensor

assembly and

check

that no

components

are

touching the enclosure. Restore power and allow

assembly including the spacer washer.

a minimum of 30 minutes for stabilization before

8.

Install the sensor assembly into the enclosure and

adjustment.

tighten firmly.

4. Connect a DVM across TP10 and GT1 on the

9.

Reconnect the sensor harness to the transmitter,

transmitter assembly. Figure 7-12

install the transmitter into the housing and restore

5.

Locate

the

gain potentiometer

which

is on

the

power.

sensor electronics directly behind one of the holes

10.

Allow one hour for the sensor to stabilize prior to

in the

sensor

body.

The

potentiometer

is

recalibration.

accessible by inserting a jewelers screwdriver

11.

Recalibrate the sensor module.

through the hole in the sensor.

7.9.3.3

SENSOR OUTPUT ADJUSTMENT

6. Determine the correct value to be read at TP10

based on the following formula:

The following procedure is to be used when, during

VTP10 = 2(C/R) , where C = concentration of span gas,

normal calibration of a new sensor, the span voltage

and R = range of detection (100 PPM). The value

cannot be adjusted to a high enough level.

is negative for all models except 5100-06, and

5100-19.

SERVICE

Page:

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