ABB TB82PH Instructions d'exploitation télécharger pdf (Page 5)

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

PRINCIPLE OF OPERATION

The TB82EC Four-Electrode Conductivity

FOUNDATION Fieldbus Transmitter provides on-line

measurement of liquid properties in industrial

environments using an advanced microprocessor-

based technology. Transmitter power and digital

communication based on the FOUNDATION Fieldbus

protocol is provided by fieldbus wiring. The TB82EC

transmitter can be installed indoors or outside due to

its IP65 and NEMA 4X environmental enclosure

ratings. Cable glands for field wiring ensure adequate

sealing barriers to ambient conditions while

maintaining the environmental ratings of the

transmitter.

The Human Machine Interface (HMI), shown in Figure

2, consists of a tactile keypad having four universal

keys, one hidden key, and a custom LCD. The LCD

has a three and one-half digit numeric region that

displays the process variable, a six-digit alphanumeric

region that displays secondary information and

programming prompts, and several status-indicating

and programming icons. Each of the four universal

keys is located under a set of icons. In each of the

instrument modes and states, one icon over a given

key will be illuminated and will represent that key’s

function. These assignments vary and depend upon

the programming mode or state the transmitter is

currently occupying. In addition to the key

assignments, text strings located in the six character

alphanumeric field are used as programming prompts.

HOLD

SPIKE

FAULT

Figure 2 – TB82PH HMI

The signal conditioning circuitry contained in the

transmitter is designed to process voltage and current

measurements generated by ABB’s four-electrode

conductivity sensors. This circuit processes the

sensor signal into a format that is transferred to a

secondary circuit. The secondary circuit uses a

microprocessor to compute the precise primary

variable compensating for the combined effects of

circuit tolerances, sensor calibration information, and

temperature effects. Permanent memory stores

transmitter and sensor specific information such as:

- Non-modifiable data such as the serial number, the

UID (Unique Identifier), the manufacturer's name and

device type, the hardware and software version of the

electronics.

- Modifiable data such as transmitter configuration

information, sensor calibration data, and security

passwords.

The sensor and all electronic parts are galvanically

isolated from the transmitter body. This isolation is

verified at the factory using a Dielectric Strength Test.

The instrument consists of three functional circuits

that have been divided into three unique Printed

Circuit Board (PCB) assemblies:

• Signal Conditioning Input Assembly

• Microprocessor/Display Assembly

• Power Supply/Communication Assembly

A block diagram representing the electronic functional

areas is shown in Figure 3. The flow of information

starts from the sensor input and moves through the

transmitter to the FOUNDATION Fieldbus interface

that produces a digital signal compliant with

FOUNDATION Fieldbus specification (IEC-61158-2 -

see Supplementary Documentation). The digital

communication and HMI capabilities provide for

remote or local access to transmitter parameters for

configuration and maintenance operations.

The fieldbus furnishes transmitter power and can be

configured as a point-to-point, tree, Daisy Chain, or

Trunk/Spurs network. Modulating the base quiescent

current generates the communication signals. The

quiescent current value is used as a reference in

order to establish the number of devices that can be

installed on a single bus line.

Data is transmitted over the bus using the digital, bit-

synchronous Manchester II coding at a baud rate of

31.25 kbit/sec. Figure 4 shows an example of a

typical bus configuration using ABB’s FIO100

interface module.

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ABB TB82PH Instructions d'exploitation Page 5

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