ABB TB82PH Instruções de Operação descarregar pdf (Página 44)

I-E67-TB82FF-2A February 13, 2002

Sensor Group C also indicates a potentially bad

process calibration or poorly performing sensor.

Again, a bad calibration will be reported, and the user

returned to the beginning of the calibration cycle.

For temperature, a bad calibration will be reported

and calibration values will not be accepted for Slope

values that are less than 0.2 or greater than 1.5 and

Offset values that are less than -40

C or greater than

+40

C. As with conductivity, temperature calibrations

use smart software routines that automatically adjust

the Slope, Offset, or Both values based on the

calibration value being entered and calibration history

if it exists.

Additional Diagnostic Messages

Other diagnostic messages may appear during

transmitter programming. These messages include

BAD.VAL (bad value) and DENIED.

BAD.VAL indicates the attempted numeric entry of a

value that is out of the allowed transmitter range. See

the Specification Section for transmitter range limits.

DENIED indicates incorrect entry of a security

password. See the Security Mode section for more

information.

SENSOR TROUBLESHOOTING

If the sensor is suspected of being the source of

problems, a quick visual inspection in many cases will

identify the problem. If nothing can be seen, a few

electrical tests using a digital multimeter can be

performed to determine if the sensor is faulty. Some

of these tests can be performed with the sensor either

in or out of the process stream.

Visual Sensor Inspection

Remove the sensor from the process and visually

check the following:

Sensor body

Inspect the sensor body for cracks and distortions. If

any are found, contact your local ABB representative

for alternative sensor styles and materials.

Cable and connectors

Inspect the sensor cable for cracks, cuts, or shorts. If

a junction box and/or extension cable are used, check

for moisture, oil, corrosion, and/or particulates where

connections are made. All connections must be dry,

oil-free, corrosion-free, and particulate-free. Even

slight amounts of moisture, corrosion, and particulates

can short sensor signals and affect conductivity

readings. Check to see that all wiring is dry and not

shorting against any metal, conduit, or earth grounds.

O-ring seals

Inspect the sealing O-rings for attack by the process

liquid. If the O-rings show evidence of corrosion,

distortion, or deterioration, contact your local ABB

representative for alternate material choices.

Sensor Electronic Test

Conductivity sensors can be electronically tested to

verify the integrity of the sensor and cable. The

sensor leads and automatic temperature compensator

leads must be disconnected from the transmitter

before any tests can be performed. Additionally,

these tests require a Digital Multimeter (DMM) that

has a conductance function capable of 0 to 200 nS

and a resistance function capable of 0 to 20 kohms.

The temperature sensor can be tested with the sensor

in the process and is tested using the following

procedure:

1. Check the resistance of the Temperature Sensor

by measuring the resistance between the yellow and

blue Temperature Compensator leads.

For a 3 kohm Balco RTD, the expected resistance

can be calculated using:

3000*1)+0.0045)*25)-(((T=

where T is in degrees Celsius. The measured

resistance should be within the expected value by ±

15%.

For a Pt100 RTD, the expected resistance can be

calculated using:

0.385)*(T+100=

where T is in degrees Celsius. The measured

resistance should be within the expected value by ±

5%.

For the 4.75 kohm Network, the expected resistance

can be calculated using:

*06-3E+

*0.0026-

0.774+T*104.5-6329=

432

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