Yokogawa 415 User Manual

GAS & STEAM

FLOW COMPUTER

MODEL 415

6 December 1999

CONTENTS

List of Symbols

1. Introduction 7

1.1 Model Number Designation 9

2. Specification 10

3. Operation 14

3.1 Front Panel Operation 14

3.2 Flow Equations for Gases 16

3.2.1 Ideal Gas Law 22

3.2.2 General Gas 24

3.2.3 Natural Gas 25

3.3 Steam Measurement 26

3.4 Filtering 31

3.5 Non-Linearity Correction 33

3.5.1 Digital Input Linearity Correction 33

3.5.2 Analog Input Linearity Correction 35

3.6 The Output Pulse 37

4. Options 39

4.1 The 4-20mA Output Option 39

4.1.1 Load Specification 40

4.1.2 Calculation 40

4.2 The RS232/422/485 Interface Option 43

4.2.1 Hardware 43

4.2.2 Multipoint Communication 44

4.2.3 Communication Protocol 46

4.3 Data Logging 48

4.4 The Relay Output Option 49

5. Calibration 50

5.1 Programming Chart 52

5.2 Definitions 59

6. Input Circuits 62

6.1 Frequency Flow Input 62

6.2 Analog Inputs 67

6.3 Remote Switches (Model 415A Only) 70

7. Installation 71

7.1 General 71

7.2 Wiring Designations for the Mode 415 73

Appendix 75

Properties of Selected Gases 75

Index 77

List of Symbols Used in this Manual

Symbol Description SI Units US Units

A Normalised signal from the

flowmeter which will be 0 at 4mA and 1 at 20mA.

G Specific Gravity for Gas.

Specific Enthalpy at Reference

kJ/kg kJ/kg

Conditions.

Specific Enthalpy at Flow

kJ/kg kJ/kg

Conditions.

K-factor (pulses/unit) for a

pulses/m

frequency flowmeter.

N Timebase Constant with which the

flowrate is displayed and is:

1 for units/second

60 for units/minute

3600 for units/hour

86400 for units/day

Density at base conditions. kg/m

Density at flow conditions. kg/m

Pressure at base conditions. kPa (abs) psia

pulses/ft

lbs/ft

Critical pressure of gas. kPa (abs) psia

Symbol Description SI Units US Units

Pressure at flow conditions. kPa (abs) psia

Energy value of steam. MJ/day

BTU x 1000/day

MJ/hr

MJ/min

BTU x 1000/min

MJ/sec

Mass Flowrate. kg/day

kg/hr

kg/min

kg/sec

Volume Corrected Flowrate. m3/day

/hr

/min

/sec

Note: If the corrected flowrate is at standard base conditions, then the flow will be in scm or scf (ie. standard cubic meters or feet).

If the corrected flowrate is at normalised base conditions, then the

flow will be in Nm Span (Mass Flowrate at 20mA). kg/day

(ie. Normalised cubic meters).

kg/hr

kg/min

kg/sec

BTU x 1000/hr

BTU x 1000/sec

lbs/day

lbs/hr

lbs/min

lbs/sec

/day

/hr

/min

/sec

lbs/day

lbs/hr

lbs/min

lbs/sec

Span for a volumetric flowmeter (eg

vortex).

m3/day

/hr

/min

/sec

/day

/hr

/min

/sec

Symbol Description SI Units US Units

Span (Volumetric Flowrate at

20mA) and at base conditions.

Temperature at base conditions. °K

m3/day

/hr

/min

/sec

(Kelvin)

Critical temperature of gas. °K °R

Temperature at flow conditions. °K °R

Specific Weight of Steam at

Reference Conditions.

Specific Weight of Steam at Flow

Conditions.

Compressibility at base conditions.

Compressibility at flow conditions.

dm3/kg dm3/kg

/day

/hr

/min

/sec

°R

(Rankin)

Introduction 7

1. INTRODUCTION

The Model 415 Gas Flow Computer incorporates compensation for gas and vapours to the following equations:

1. Ideal Gas Law using temperature & pressure correction, but where compressibility is ignored.

2. General Gases where compressibility is calculated using the

Redlich-Kwong

3. Natural Gas using NX-19

equation.

equation for supercompressibility.

4. Steam Equations for both saturated and superheated steam. Mass and energy flowrates are calculated using standard equations to determine the specific weight and enthalpy of steam.

Inputs from a wide range of flowmeters are handled including vortex, turbine, orifice plate, averaging pitot tubes, wedges, V-Cones and target flowmeters. In addition, where two differential pressure transmitters are used across an orifice (or similar device) to increase the measured flowrange, both D.P. transmitter inputs can be accepted into the Flow Computer and scaled separately with automatic crossover.

Options include a 4-20mA re-transmission, high and low flow alarms and an RS232/422/485 output. A unique feature available with the RS232/422/485 output is the ability to print flowrates and totals at programmable time intervals. This enables the instrument to function as a data logger when used in conjunction with a printer, or other storage device.

Two versions of the instrument are available, the Model 415R with direct RTD input, and the 415A with a 4-20mA temperature input. Both accept a 4-20mA pressure input.

The Model 415 is designed to supersede the Models 405GS and 405ST.

Redlich & Kwong. "An equation of State". Chem Rev, vol 44, p233, 1949.

Par Research Project NX-19. "Extension of Range of Supercompressibility Tables", American Gas Association, 1962.

8 Introduction

This instrument conforms to the EMC-Directive of the Council of European Communities 89/336/EEC and the following standards:

Generic Emission Standard EN 50081-1 Residential, Commercial & Light

Industry Environment.

Generic Emission Standard EN 50081-2 Industrial Environment.

Generic Immunity Standard EN 50082-1 Residential, Commercial & Light

Industry Environment.

Generic Immunity Standard EN 50082-2 Industrial Environment.

In order to comply with these standards, the wiring instructions in Section 7.1 must be followed.

Introduction 9

1.1 MODEL NUMBER DESIGNATION

The Model number of an instrument describes which input and output options are installed and the AC mains voltage rating.

Model 415 R. 1 0 E C

C for Conformal Coating

E for 220/240 VAC A for 110/120 VAC

D for DC Power Only

Temperature Options

R for RTD input 0 for no option A for 4-20mA 1 for 4-20mA output

2 for RS232/422/485 3 for Relay option 4 for 4-20mA and relays 5 for RS232/422/485 and relays

Mounting

1 for panel mounting 2 for field mounting 3 for explosionproof

The Model number of the instrument is displayed on first entering the Calibration Mode (see Section 5).

10 Specification

2. SPECIFICATION

General

Display: Alphanumeric LCD display with

backlighting and 2 lines x 20 characters/line.

Each character 5.5mm high. Keyboard: Sealed membrane keyboard with four keys. Transducer Supply: 8-24VDC field adjustable, 65mA maximum. Power Requirements: 14 to 28.0 VDC, 300mA typical.

AC mains - Set internally to 95 - 135 VAC

or 190 - 260 VAC. Operating Temperature: 0 to 55°C. Facia: Watertight to IP65 or Nema 3S. Dimensions: 144mm (5.7") wide x 72mm (2.8") high x

188mm (7.4") deep.

Depth behind Panel: 139mm (5.5") x 67mm (2.6").

Frequency Input

Frequency Range: Minimum: 0.25Hz on Rate.

0Hz on Total.

Maximum: 10KHz.

Input Circuits: Will accept most sine logic and proximity

switch inputs (see section 6.1). K-factor Range: 0.1000 to 999,999. Non-Linear Correction: Up to 10 correction points.

Specification 11

4-20mA Inputs

Inputs: Flow (2), pressure & temperature. Input Impedance: 250 ohms. Measurement Ranges: Pressure: 0kPa (abs) (0 psia) to 100,000 kPa

(10,000 psia).

Temp:-273°C (-459.4°F) to 1200°C (2192°F). Accuracy: 0.05% Circuit: The 250 ohm resistors are connected to a

common signal ground (current sinking). Span (Flow): 999,999.

RTD Input (Model 415R)

Temperature Measurement Range: -100°C (-148°F) to 200°C (392°F),

Note: a wider temperature range can be

handled via a 4-20mA input. Accuracy: 0.1°C RTD Type: Platinum PT100. Linearity: The non-linearity of the RTD is internally

compensated for.

Pressure Input

Type: Absolute or Gauge. Span: The absolute or gauge pressure at both 4mA

and 20mA is programmable. Atmospheric: If a gauge pressure sensor is used the

atmospheric pressure can be programmed.

4-20mA Output

Function: The flowrate selected as the Default display

is output on the 4-20mA output. Resolution: 10 bits. Accuracy: Better than 0.1%. Maximum Load: 500 ohms internally powered.

950 ohms from 24 VDC. Isolation: Output is isolated.

12 Specification

Relay Output

Function: High and low flowrate alarms based on the

flowrate selected as the default display. Maximum Switching Power: 1250VA. Maximum Switching Voltage: 250 VAC, 30VDC. Maximum Switching Current: 5 Amps.

RS232/422/485 Option

Type: Both RS232 & RS422/485 are provided. Function: Printer and computer protocols are

programmable. Output: Output is on request or at a programmable

time interval. Baudrate: 300 to 9600. Data Bits: 7 or 8. Parity: None, Odd, Even.

Pulse Output

Function: The pulse output is scaled and outputs one

pulse each time the Default total increments

by one digit. Pulse Width: 10mSec (negative going pulse). Duty Cycle: Maximum of 49 pulses per second. Output: An open collector transistor will sink 100mA

maximum.

Ideal Gas

Display: Corrected Volume (m

or ft3).

Mass (kg or lbs). Temperature Range: -273°C (-450°F) to 800°C (1472°F).

(RTD has a more limited range.) Pressure Range: 0 kPa abs (0 psia) to 100,000 kPa (10,000

psia).

Specification 13

General Gas

Gases: Handles most gases for which the critical

temperature, pressure and SG are known.

Compressibility: Calculated using Redlich-Kwong equation.

Display: Corrected Volume (m

or ft3).

Mass (kg or lbs).

Temperature Range: -273°C (-450°F) to 800°C (1472°F).

(RTD has a more limited range.)

Pressure Range: 0 kPa abs (0 psia) to 100,000 kPa (10,000

psia).

Natural Gas

Calculations: Uses NX-19 equation to calculate

supercompressibility Fpv.

Displays: Corrected Volume (m

or ft3).

Mass (kg or lbs). Temperature Range: -40°C (-40°F) to 115°C (240°F). Pressure Range: 101.325 kPa (14.69 psia) to 34,380 kPa (4985

psia). SG Range: 0.554 to 1.000. Carbon Dioxide: 0 to 15% mole. Nitrogen: 0 to 15% mole.

Steam

Displays; Mass (kg or lbs)

Energy (MJ or BTU x 1000). Calculations: Uses 1967 IFC Formulation equations to

calculate specific weight and enthalpy of

steam. Steam Type: Saturated and Superheated. Temperature Range: 20°C (68°F) to 800°C (1472°F).

(RTD has a more limited range.) Pressure Range: 1 kPa (abs) (1 psia) to 100,000 kPa (10,000

psia).

14 Operation

3. OPERATION

The Model 415 uses a low power CMOS microprocessor to perform all measurement and control functions.

The instrument is fully programmable with all operating parameters and calculation constants user programmable (see Section 5 entitled Calibration for information on programming). All parameters and constants are stored in a non-volatile memory which retains data without battery backup for a minimum of 10 years.

3.1 FRONT PANEL OPERATION

The alphanumeric display provides a clear indication of which parameter is displayed and the engineering units.

During Calibration, the value which is to be normally displayed can be programmed as the DEFAULT display. For example, if Mass is required and is programmed as the DEFAULT display, then pressing the RATE key will show the Mass flowrate, and pressing the TOTAL key will show the Mass total.

The scaled pulse out, 4-20mA output option and high/low alarm option are also based on the DEFAULT display selection. For example, the 4-20mA output would be a re-transmission of the Mass flowrate, if the DEFAULT display is set to Mass.

The DISPLAY key can be used to step through the data which can be displayed, as follows:

Gas Flow

Corrected Volume (Rate & Total) Mass (Rate & Total) Temperature & Pressure

Operation 15

Steam

Mass (Rate & Total) Energy (Rate & Total) Temperature & Pressure Specific Weight & Enthalpy

If any value other than the default display values are selected, they will remain displayed for 5 seconds, after which the display will automatically revert to the default values.

Totals are displayed with a maximum of 8 digits, including decimals. For example, if two decimals are programmed, the maximum total is 999,999.99, after which the totals roll over to zero and continue counting.

For large flowrates, totals can be integrated at 1/1000 of the flowrate by programming the Total Units function at x 1000. The units of measure will then be displayed as follows:

SI Units

Rate Total

cm/h kcm scm/h kscm Nm

kNm

kg/h tonne MJ/h GJ

US Units

Rate Total

cft/h kcft scft/h kscft lbs/h klbs BTU x 1000/h MBTU

(Note: k = x 1000, M = x 1,000,000, G = x 1,000,000,000).

The RESET key can be used to reset the totals whenever one of the totals is displayed. Both totals will be reset at the same time. The RESET switch can be disabled during calibration to prevent front panel resetting.

16 Operation

3.2 FLOW EQUATIONS FOR GASES

This section applies only to gas flow measurement and, if the Model 415 is to be used for steam measurement, the reader can skip this section and go to section

3.3.

The Model 415 will accept inputs from a wide range of flowmeters with the flowrate calculated by the equations defined below. Both mass flow and volume corrected flow to a base temperature and pressure are calculated and displayed in either SI (metric) or US units. For an explanation of the symbols used in the equations see the list at the beginning of this manual.

Two basic formulae are common to all equations:

1. Specific Gravity, G =

2. Density of a Gas,

MolecularWeight ofGas

MolecularWeight ofAir

MolecularWeight ofGas

.....(1)=

at base conditions:

In SI Units

3.4834 G P

kg/m

In US Units

2.6988 G P

ZBT

Standard Conditions

Standard conditions are defined as:

15°C (288.15°K) and 101.325 kPa

or 59°F (518.67°R) and 14.69595 psia.

ZBT

28.9625

lbs/ft

.....(2)

.....(3)

Normalised Conditions (SI Units only)

Normalised conditions are defined as:

0°C (273.15°K) and 101.325 kPa.

A. Volumetric Flowmeters With Frequency Output.

eg. Vortex, turbine or positive displacement flowmeters.

Operation 17

N. frequency(Hz)

......(4)Q

......(5)QM= ρB.Q

B. Volumetric Flowmeters With 4-20mA Output.

eg. Vortex, turbine or positive displacement flowmeters with frequency to current convertors.

VB=SV

QM= ρB.Q

......(6)

C. Differential Pressure Flowmeters With 4-20mA Output And A Square

Law Relationship.

eg. Orifice Plates, Averaging Pitot Tubes, Target Flowmeters, etc.

VB=SVB

QM= ρB.Q

......(7) Q

18 Operation

D. Differential Pressure Flowmeters With 4-20mA Output And With A

Linear Flow Relationship.

eg. D.P. transmitters with a square root extractor or VA meters.

VB=SVB

......(8)Q

QM= ρB.Q

Note that the pressure and temperature are still square rooted, even though the flow signal A is not. This is because the output from the D. P. transmitter is not truly volumetric, but will be affected by a change in density of the gas being measured. Therefore, the equations relating to differential pressure will apply.

E. Dual Differential Pressure Flowmeters With 4-20mA Output.

To increase the range over which flow can be measured, two D. P. transmitters with different spans can be connected across a common orifice or other differential pressure device.

Equations 5 & 6 or 7 & 8 above would be used depending upon whether the D. P. transmitters have square root extractors. Separate scaling using these equations is then programmed for each transmitter.

At lower flowrates, transmitter 2 will be used as a basis of measurement and at higher flowrates, transmitter 1 will be used. The crossover point will occur when the input on transmitter 2 exceeds 20mA.

Operation 19

Example 1

Flow is to be measured across an orifice in the range of 0 - 2000 scm/hr. Because flow needs to be measured over a 10:1 range, two transmitters are spanned as follows:

Transmitter 2 0 - 600 scm/hr Transmitter 1 0 - 2000 scm/hr

Hence, above 600 scm/hr, transmitter 2 is used and below 600 scm/hr, transmitter 1 is used. Since D. P. transmitters are accurate over a 3:1 range, then the system will provide reliable readings between 200 to 2000 scm/hr, which is a 10:1 turndown.

Both transmitters will be individually scaled to equations 5 & 6 or 7 & 8, as appropriate.

PROGRAMMING THE FLOW COMPUTER

For equations 4 to 8 to work correctly, a number of parameters need to be programmed:

K-factor (for frequency producing flowmeters)

(or SM) Span (for analog flowmeters)

Base temperature Base pressure

G Specific Gravity of Gas

The flow computer will measure the flow input A (normalised between 0 and 1), the temperature, T

, and pressure, PB. Depending on the gas

equation selected, the compressibility factors and density are then calculated. Other parameters must also be programmed and these are fully detailed in section 5.

20 Operation

PROGRAMMING THE SPAN AS MASS

It is also possible to enter the span of an analog flowmeter in mass (instead of volume) at a nominal flowrate. The flow computer will then automatically calculate the Span, S as:

Example 2

If a flowmeter produces 1000 kg/h at 30°C and 220 kPa, and the specific gravity is 1.52 then from equation (2)

3.4834 x 1.52 x 220

ρ =

1x(30 + 273.2

, for corrected volume flow

)

......(9)

(assuming ZB = 1)

= 3.84 kg/m

Therefore, from equation (9)

1000

3.84

= 260 m

/hr

If the span is programmed as mass SM = 1000 kg/hr, with the base temperature programmed to 30°C and the base pressure programmed to 220 kPa, then the flow computer will display both mass (kg/hr) and volume (m

/hr) corrected to a base condition of

30°C and 220 kPa.

and

Operation 21

Example 3

If the mass flow is defined at non- standard base conditions and it is required to display the corrected volume at standard conditions, then it is first necessary to convert the mass to an equivalent mass at standard conditions.

Using example 2 for a differential pressure device, the corresponding mass at 15°C and 101.325 kPa can be determined from equation 7 as:

M1=SMB

where SM1 = the new span at 15°C and 101.325 kPa

with the input A = 1

Therefore, the new span S

= 1000 x

, with ZB = Z1= 1, is:

101.325 220

30 + 273.2 15 + 273.2

= 696.1 kg/hr

Hence, the span would be programmed as 696.1 kg/hr, the base temperature as 15°C and the base pressure as 101.325 kPa. The corrected volume will now be displayed at standard conditions.

22 Operation

3.2.1 Ideal Gas Law

If the effects of compressibility on a gas can be ignored, then Z

and ZF can be set

to 1.00 in equations 1 to 8. This can make calculations much simpler, particularly when the properties of a gas are not known or, over small ranges of pressure and temperature, where the effects of compressibility are often negligible.

Example 4

A vortex meter is used to measure oxygen in a 2" pipe at 25° C and 200 kPa (abs). The flowmeter produces 9500 pulses/m flowrange is 100 to 1000 m

/h. Determine the flow parameters

and the

which need to be programmed into the instrument for it to display the flowrate and total flow as both mass and corrected volume to Standard Conditions.

From the table, the Molecular Weight of oxygen is 31.9988. From equation (1)

31.9988

28.9625

= 1.105

According to ISO5024, Standard Conditions are 15° C (59° F) and

101.325 kPa (14.69595 psia). Hence, the following are programmed into the instrument:

Scaling Factor (K-factor) = 9500 pulse/m

Specific Gravity G = 1.105 Base Temperature = 15 °C Base Pressure = 101.325 kPa Timebase of Rate = Hours

Other parameters can be programmed as required.

The instrument will now display the corrected volume and mass flowrates of the gas.

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