Precision Measuring PD 340 Flow Transmitter

PD 340

Introduction

The PD340 flow transmitter is a precision meter for the volumetric measurement of liquids which are electrically conducting. The transmitter can be used in applications where a hygienic design is required. The rugged construction of the transmitter makes it suitable for installations where solids particles are in the liquids. The PD340 transmitter is equipped with a microprocessor controlling and supervising all of its functions.

Functions

Construction

fig.1:Structure The PD 340 flow transmitter consists of three parts: meterhead, electronic module, and terminal box. The electronic module and the terminal box are the same for all sizes of transmitters.
The Meterhead consists of a stainless metering pipe with clamp liners. Two magnet coils are mounted external to the metering pipe. inside the metering pipe two stainless electrodes are mounted. the measuring section is designed so that changes in flow profile do not affect meter accuracy hence the transmitter has a wide range of flow rates within its linear accuracy. Changes from laminar to turbulent flow do not affect the linear accuracy and changing viscosity has no effect on meter accuracy. The calibration of the meterhead is carried out using a computer controlled calibration facility.
The Electronic Module is micro-processor based and both controls the sequence of measurement and output signal transmission.
The use of the micro-processor has enabled a compact design to achieved yet including many functions. The electronic module is available in two versions, standard and extended.
The standard version has two pulse outputs and can be directly connected to a display unit.
In the extended version, one of the pulse outputs can be changed into analogue output, 4-20mA. Besides, it is possible to connect the transmitter to a data network for central processing.
The Terminal Box is completely separated from the electronic module. hence connections can be changed without disruption to the electronics. All terminals in the terminal base are clearly marked with both number and functions. The box is also equipped with 3 cable glands, PG 11.

Operating Principles

fig.2 Operating Principles The meterhead consists of metering pipe with two magnetic coils. When a current is applied to the coils a magnetic field is produced at right angles to the metering pipe.
With a conductive liquid flowing through the metering pipe an electrical voltage is inducted and measured by two electrodes mounted in the metering pipe. This voltage is proportional to average velocity of flow and therefore to the volume flowing.
The micro-processor in the transmitter controls the current generator keeping the magnetic field constant. The voltage of the electrodes is taken via an amplifier and signal converter to the micro-processor which calculates the liquid flow.

Specification


fig.2 Operating Principles

Deviation flow measurement: Less Than ±0.% of max. flow.
Deviation current output: Cf. fig 3, plus ±0.3% of range for current output.
Ambient temperature effect: Less than 0.04%/10oC.
Voltage supply effect: Less than 0.01%/10oC.
Response time: 0.2 sec. on pulse output,
1 sec. on current output
Max. capacity: 
PD 340 - C25:  8m3/h.
         C38: 20m3/h.
         C51: 40m3/h.
         C63: 80m3/h.
Measurement of Temperature: 
Deviation: Less than ±0.9oC with Pt-100 detector Din 43760.
Limits:    From -30oC to +100oC.
Ambient temperature: From -10oC to +50oC.
Power supply: 24V AC ±15%, 50/60 c/s or 24V DC ±15%.
Power Consumption: Max. 6W
Liquid: 
Conductivity: Min. 5΅s/cm.
Temperature:  From -30oC to +100oC
Pressure:     Max. 10 bar.
Output: The transmitter can give two different output signals, pulse signal or current signal. External voltage supplies are required for both types of signals.
Pulse signals: Pulse Signal
Current signal: Current Signal
Material: 
Electrodes:    Stainless steel AISI 316.
Metering pipe: Stainless steel AISI 316.
Coating inside metering pipe: Teflon.
Housing:       PPO Noryle.
Connections: Clamp pipe coupling DS/ISO 2852

Size Of Meter

fig.4 Size of transmitter The dimensions of the meterhead should be selected on the basis of liquid flow, the smallest possible transmitter is selected for given maximum flow rate. This will ensure optimal accuracy of measurement.
If the metering section is smaller than the pipework in the installation the connection pieces should be tapered.

Location Of Transmitter

fig.5 Mounting of Transmitter The transmitter should be located in the piping system so that the metering pipe is always filled with liquid as the transmitter can register flow even if the metering pipe is empty. As the transmitter sees air in the liquid as a volume, the volume of air in the liquid must be reduced to a minimum, and the transmitter should be located in the piping system, at the point of maximum hence the influence of air on the measurement will also be minimum.
If the transmitter is located downstream of a pump which may suck air during the measuring period an air eliminator should be mounted upstream of the transmitter.
The transmitter can be mounted both horizontally and vertical. Air elimination must always be guaranteed. The positive flow direction is indicated by an arrow on the meterhead.
To create the best conditions for precise metering a straight run of least 3xD should be mounted upstream and downstream of the transmitter. When selecting the location of the transmitter it must be ensured that the ambient temperature is kept within the specified limits. Finally, the transmitter should be located so that the electronic box and the terminal box can be dismantled and mounted on site.
The transmitter should always be electrically connected thus preventing condensation in the electronics.

Output Signals

fig.6 Connections The transmitter has three outputs, OUTPUT 1,2 and 3.
OUTPUT 1 is power supply output, which can be used for power supply of external counter circuit. the voltage of the output can vary from 20 to 32V DC.
OUTPUT 2 can be selected for one of three functions:
  1. Pulse signal, 0-5 c/s. The signal is taken to a counter, electronic or electromechanical, for indication of the total volume, e.g. in litres.
  2. Sign for OUTPUT 3. The signal indicates the flow direction and can be taken to an UP/DOWN counter, which is actuated by pulses from OUTPUT 3.
  3. The output signal from the pre-set counter. before start of measuring a SET-point via the display is inserted, and the pre-set counter is reset. When the required volume is achieved, OUTPUT 2 gives a stop signal.
OUTPUT 3 can be selected for one of two functions:
  1. Pulse signal 0-1000c/s. The signal can for instance be taken to a counter for volume registration.
    The signal can also be used for registration of actual flow.
  2. Current signal 4-20mA (only for transmitter in extended version). The signal can be taken to regulator for controlling the liquid flow.
Beside these three outputs it is possible to connect the flow transmitter direct to the display unit PD 210. It is also possible to connect the extended version transmitter to a communication system for data processing.
Pre-selection, Total Volume, Temperature, Flow Registration, Flow Control.

Display Unit

fig.7 Display Unit Introduction:
The display unit PD 210 can be connected direct to the transmitter. The display unit can be used as an accumulative counter and pre-set counter and for the registration of instantaneous values of flow rate and temperature. The display unit is also used in connection with fault finding.

Functions:
Accumulative Counter: The display unit registers the total volume, e.g. in m3
Pre-set Counter: Before commencing measurement a SET-point is inserted, and the pre-set counter is reset manually. When the required volume is achieved, OUTPUT 2 gives a stop signal.
Instantaneous value, flow: The display unit registers the actual flow rate, e.g. in m3/h.
Instantaneous value, temperature: The display unit registers the actual temperature in oC.
Fault finding: The flow transmitter is equipped with a comprehensive test system which is able to disclose faults, arising from improper use of the transmitter, or faults arising from the transmitter during use. When the test system registers a fault, an »A« appears in the first digit of the display. By pressing the »TEST« button the display will register an error checking code of two digits, registering the type of error.
Connection:
The display unit is connected to the flow transmitter with one double-connected cable. The display unit is supplied with power via this cable. It also transmits the exchange of data between the flow transmitter and the display unit. The length of the cable must not exceed 100m.
Location:
The display unit is intended for fixed installation e.g. in a panel. The unit is waterproof. The ambient temperature limits are -10oC to +50oC.
Dimensions: fig.8 Dimensions
Tel: (01704) 505333 Fax: (01704) 505334
E-mail:sales@instruments-gauges.co.uk