Hart communicator's function

Hart communicator’s mostly used functions in calibration of a device

LSV= lower set value:

The minimum range value of device, it can measure

USV=upper set value:

The maximum value of device , it can measure

LRV=lower range value:

The minimum value to which device has to read it as 0%

USV=upper range value

The maximum value to which device has to read it as100%

Sensor zero trim:

To zero the sensor value (means which output is generating sensor to zero it)

D/A trim=digital to analog trim:

To zero the out put of transmitter,to generate the 0% out put at that state of the device

calibration of transmitter

Calibration of a pressure transmitter

Calibration with analog apparatus

Equipment

Pressure Transmitter range (0 to 200 psig )

Pressure source range (0 to 250 or more than)

Multi meter

24vdc power supply

Procedure

Set range of transmitter to required range (0 to 200 psig)

Connect multi meter in series of power supply to the transmitter

Make graduation of the range of transmitter as follows

(for 0 to 200 psig range)

Applied pressure	Multi meter output	%age
0 psig	4 ma	0%
50 psig	8 ma	25%
100 psig	12 ma	50%
150 psig	16 ma	75%0
200 psig	20 ma	100%

First adjust the zero (with zero screw) that multi meter must read 4ma

If multi meter is reading less then 4 ma then increase the out put by clockwise moving to the zero set screw

And if multi meter is reading more than 4 ma then decrease the out put by moving the anticlockwise to zero set screw

After adjusting the zero apply 50 psig pressure (as u made graduation) to the transmitter where multimeter must show 8ma if not then adjust it from span screw

After adjusting check

100 psig = 12ma.

150 psig = 16ma

200 psig = 20ma respectively

after adjusting all the readings check two or more time to all readings if no changes occur then your transmitter is calibrated

Calibration with HART communicator (Highway addressable remote transducer)

Equipment

Pressure Transmitter range (0 to 300 psig ) “must be Hart enabled”

Pressure source range (0 to 350 or more than)

Hart communicator (275/375)

24vdc power supply

Procedure

Connect the Hart communicator with the transmitter

Connect its terminals across the 250 Ohms resistor connected in series of power supply to the transmitter

When Hart communicator detects your device then go into its setup

Adjust the range through the option lower/upper range value

Set lower range value to zero (0) and upper range value to 300 psig

Set the zero by zero trim option (given pressure must be zero)

Apply 300 psig pressure to the transmitter and set it the 100% range value of transmitter by span trim option

After this setting check the 0 and 100% out put by connecting also multi meter in the series of the power supply

At 0 psig pressure multi meter must read 4ma

Apply the 300 psig where multi meter must read 20ma

Repeat this practice two or three times your transmitter will be calibrated when it matches its output reading match to the input

What is Fusible Loop

What is a fusible loop charge panel? A fusible loop charge panel is a pneumatic panel that monitors a fusible loop system for the detection of fire. Fusible loop system are installed on offshore platforms to detect fire. The installation of the fusible loop are in accordance with API RP 14C recommendation.

The charge panel will regulate and meter a fix amount of instrument air to the fusible loop. During a fire, the heat generated by the fire will melt one or more of the fusible plug located in or near the fire. The 'melting' of the plug will cause a release of air from fusible loop through the plug. Since the release of this regulated air exceeds the amount of regulated/metered air supply, the pressure in the loop will decrease significantly. This decrease in pressure is monitored by a pressure switch on the charge panel. The signal from the switch is then utilized to signal an alarm to the Fire and Gas System.  In addition, an additional pneumatic output is tied to the deluge valve pilot valve where it is use to open the deluge valve.

Reference: http://www.emlmanufacturing.com/Instrumentation.htm

Transmitter Basics

Definition

The major purpose of a transmitter is to measure a change in process variable from a remote location and to transmit it at required location. Transmitter is a device (electronic/pneumatic) which measure a process variable and converts it into standard, proportional signal. Standard signal can be pneumatic or electronic

Pneumatic signal is 3 to 15 psig while electronic signal is 4 to 20 ma. Transmitter has a supply of 24vdc for electronic and 20 psig for pneumatic

Principle of operation

The transmitter consist of a sensor part and a processing part. The sensor part create a primary change proportional to the process variable’s change. The processor part convert that change into a standard ouput signal. For example:

A process variable e.g pressure can be varied from 0 to 100 psig and we want to measure it and also we want to transmit it to a remote location. Then first off all range of transmitter is set to our required value (o to 100 psig). Then we will apply process variable at different values as 0%, 25%, 50%, 75%, 100%. The transmitter will generate a proportional out put as 4mA, 8 mA, 2 mA, 16mA, 20 mA or if we use pneumatic transmitter 3 psig, 6psig, 9psig, 12 psig, 15 psig respectively that out put signal can be transmitted to a remote location either it is electronic or pneumatic.