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Introduction The Burela Instrumentation industrial pH sampler is an on-line sampler operating on an approximate 2 minute cycle extracting a sample from the process, cooling the sample and presenting the cooled sample to a pH electrode, then washing all wetted parts with water plus a periodic weak acid wash to maintain a clean system. This sampler is suited to applications where high solution temperatures or process composition cause premature electrode failure when direct process insertion is used. The sampler will provide a low maintenance reliable and accurate indication of process pH over a wide range of process conditions and is able to be adapted to suit most applications. pH Sample Overview The ph sampler is housed in two B&R SST enclosures supported by a 50mm SST angle frame. The larger enclosure contains all the wet parts including valves, level sensors, regulators, acid pump, sample chambers and solenoid box. The smaller enclosure houses the PLC and all the electrics. All I/O and power are connected to terminals within the electrical enclosure. Potable water is connected to a pressure regulator located at the LH side of the sample enclosure. Air, acid supply and drains are all located along the bottom of the sample enclosure. All materials used in the sample enclosure have been selected to provide maximum reliability and corrosion resistance. High quality SST, polypropylene, polyethylene & polycarbonate materials have been extensively used. All manufactured parts have been designed with ease of maintenance in mind, using O-ring sealed connections where possible and hand operated connections within the main sample train. The sampler has a range of manual operations designed to assist the maintenance technician with both fault diagnostics and routine maintenance. See Routine Maintenance section. Installation The pH samplers require the following services.
• 220 – 240VAC power at 10 Amps • Potable Water ~ 200kPa • Compressed Air (Instrument Quality) ~ 600kPa • Suitable drain line approx 40mm return to process or sump • Interface to DCS or SCADA system for 4-20mA pH signal & optional
All electrical & signal connections are terminated within the Electrical Enclosure. Mains power required by the sampler is via a 220 – 240 VAC GPO protected by an earth leakage circuit breaker (RCD installed by customer). This GPO provides electrical isolation for the sampler. Mains power (220 – 240VAC) is terminated - AC active - Terminal 6 AC neutral - Terminal 11 Earth - Terminal 15
4Amp
240
VAC
4Amp
240
VAC
4Amp
240
VAC
4Amp
240
VAC
4Amp
240
VAC
F1 F2 F3 F4 F5
PLC 24VDC
Power
Supply
24VAC
Trans
former
E&H
level
switch
acid
pump
N N N N
11 12 13 14
E E E E
15 16 17 18
PLC − N
24VDC PS − N
24VAC T
X − N
E&h LS − N
ACID PUMP − N
240 VAC SUPPLY IN240VAC − N
IN
EARTH − IN
to R
1
to e&h ls − term 1
to 24vac tx primary
to 24vdc supply in
to plc supply in
6 7 8 9 10
Digital Input & outputs from DCS or PLC control system. Digital In 1 - Terminal 30 - Sampler RUN command Digital Out 1 - Terminal 28 - Sampler Fault Status Digital Out 2 - Terminal 29 - Read pH signal flag. Digital I/O Supply Terminal 53 - +24VDC Supply Digital I/O Common Terminal 31 - 24VCD Common Analog output from pH transmitter (4 – 20mA) Analog Out - Terminal 32 - 4 – 20 mA output + Analog Out Common Terminal 34 - 4 – 20 mA common
All the sampler services are connected at the base of the wet parts enclosure.
Potable water is connected to the pressure regulator located at the lower left hand side of the enclosure. ½” NB hose secured with a worm drive hose clip or similar Vacuum Eductor drain – 3/8” tubing to 40mm drain line Sampler Drain - 3/8” tubing to 40mm drain line Instrument Air Supply - Connect to pressure regulator located at bottom right of enclosure. ¼” air line connection. Process Sampler connection as discussed below.
Process Connections: The sampler process connection will vary with customer requirements. The sample has a 3/8” polypropylene tube from its sample chamber to the sample base. Customer connection will occur here. The sample probe will usually take the form of a 20 to 25mm SST pipe of nominated length into which a polypropylene tube is inserted with suitable fitting locating the tube at either end. The SST pipe with have either a flanged or threaded adapter fitted to attach to the process vessel. It is strongly recommended that the sample probe be located at the top of the vessel to permit insertion & removal of the probe while vessel is full. The sampler is capable of lifting the sample up to 6 meters based on a SG of 1.0. Location of the probe and the sampler must be arranged so that the required lift does not exceed this distance. A drain is required to return the sample and wash water back to the process or to a returns sump as preferred by the customer. This takes the form of a 40mm PVC pipe with an open tundish arrangement at the sampler end into which the sample cone drain is directed. Do not use a close-coupled configuration for the drain as this impairs reliable draining. Sampler I/O The sampler has one binary input, two binary outputs and one analog 4 – 20mA output used for the pH signal. The binary input is used to halt the sampler PLC program from the DCS or similar by toggling a 24VDC signal. 24VDC – sample running 0VDC – sampler stopped
Binary output 1 will indicate a fault condition as detected by the PLC. This will include conditions such as- Failed to start Failed to get sample Failed to drain sample cone This is a 24VDC signal, which is rest at the start of the next cycle. Binary output 2 is the read pH signal to the DCS sample & hold module. This is a 5 second 24VDC pulse. The analog output is sourced from the E&H pH transmitter, reading the pH value. This is a 4 – 20mA isolated output. Operation & Control The sampler has a range of control and maintenance switches located next to the pH transmitter in the Electrical Enclosure. These switches are mainly used during sample maintenance. There are also 5 indicating terminals located at the top right hand side of the electrical enclosure. There functions are as follows –
• Remote / Local Switch. o Remote - Sample will run continuously when switched to Remote
providing the DCS run command (Binary In 1) is active. o Local - Sample will only respond to local switch commands and
will not post any pH readings back to the DCS. • Local Start Switch
o This will allow the sampler to do 1 cycle provided the sampler is switched to Local and the Maintenance mode is not selected.
• Pause Switch o Switching the Pause switch ON will halt the PLC program until it is
switch OFF. Used mainly for faultfinding or service functions. • Service Mode
o This switch is used to place the sample into service mode. This will only occur when the sampler is in Local and the PLC program is at the beginning of its cycle. The service mode light will illuminate when these conditions are met.
o Service mode activates the valve switches. • Manual Valve Switches
o The 8 valve, solenoid & pump switches allow manual operation of these devices when Maintenance mode is selected.
o This function allows for easy operational checks to be conducted during sample maintenance.
Sequence of Operation The sampler will run continuously while ever the run signal from the DCS is present (binary input 1) and the local / remote switch is in remote. This is a generic program and may need fine tuning during commissioning.
1. Drain sample vessel & cone – 5 secs • Transfer valve open • Drain valve open • Vent valve open • Level switches off
Ensure all wash water from previous cycle is drained from the sampler.
2. Prep Sample Line – 10 secs • Transfer valve closed • Drain valve closed • Vent valve closed • Air purge open
Remove any wash water from sample line ready for next sample
3. Electrode acid wash – 2 secs • Transfer valve closed • Drain valve closed • Electrode wash solenoid on • Acid pump on
Ensure all contaminants are removed from electrode. Electrodes soak in weak acid until step 10
4. Such up sample – 1st Vacuum – 15 secs
• Vacuum Eductor air on • Vacuum valve open • Drain valve closed • Transfer valve closed
If catchpot level switch activated then step to step 8 Sampler will make 2 attempts to get sample.
• Transfer valve open • Drain valve closed • Vent valve open • Check for sample ( sample cone level switch activated )
Check sample has activated the sample cone level switch and allow pH electrodes to stabalize. If level switch not activated – no sample alarm activated – Binary output 1.
14. Read pH – 5 secs • Transfer valve open • Vent valve open • Drain valve closed • Read pH flag on ( Binary output 2 )
Binary output 2 activated for 5 seconds to allow DCS sample and hold module to update pH valve.
15. Check Online – 1 sec • Transfer valve open • Vent valve open • Drain valve closed
16. Drain Sample Cone – 3 secs
• Drain valve open • Transfer valve open • Vent valve open
Sample is drained from sample cone
17. Rinse Sample Cone – 3 secs • Drain valve open • Transfer valve open • Vent valve open • Electrode wash valve open
18. Drain Sample Cone – 3 secs
• Drain valve open • Transfer valve open • Vent valve open
• Drain valve open • Transfer valve open • Vent valve open
27. Drain Sample Cone – 5 secs
• Drain valve open • Transfer valve open • Vent valve open
28. Fail to Drain Check – 1 sec
• Check sample cone level switch is off If level switch is on fail to drain alarm is activated – Binary output 1. Sequencer stops until blockage is cleared.
Maintenance: pH Sampler Wet Parts Layout Squitch Level Switch Solenoid Sample Enclosure Chamber Vacuum Generator Electrolyte Reservoir Transfer Valve Sample Cone Air Regulator Wash Water Valve Electrode Acid Wash Valve Pump Pressure Regulator Drain Valve The sample requires periodic maintenance to maintain reliable & accurate operation. The frequency and level of this maintenance may vary depending on the service the sample is attached to. The normal maintenance period is once a week where the following task should be undertaken. A hose is provided inside the wet part enclosure to enable water to be added to the acid container and wash down the wet parts in the event of spills or leaks.
To perform the sample maintenance, place the sample into Local and allow the current cycle to end. Switch to Maintenance mode to allow operation of the valve maintenance switches. Maintenance mode ON light will illuminate when sampler cycle ends.
• Clean & Buffer pH electrodes as per manufactures instructions. A 2 buffer check is recommended, appropriate to the pH range being used.
• Replenish acid container – nominal 10% Sulphuric Acid It is recommended that a drip tray or bund be installed under acid carboy; this could be drained back to tank.
• Check correct operation of acid pump, ensure pump & lines are free of air. Prime if necessary.
• Replenish KCl electrolyte reservoir and check reservoir pressure. Observe correct procedure for disconnecting and reconnecting airline to KCl reservoir. Refer to manufactures instructions for this procedure.
• Clean sample catchpot & sample cone of process residue as necessary. • Clean transfer & drain valves, check for wear, leaks and smooth operation.
Ensure that when valves are reassembled the ball is central in its housing to prevent stress and subsequent breakage of the valve spindle. Note that these valves have been fitted with SST balls and pactene seats to provide long valve life. Apply a small amount of silicone grease to the moving parts. The spring tension adjuster adjusts return action of the valve.
• Clean and apply a smear of silicone grease to the insulated part of the sample cone level probe. This prevents moisture tracking between the level probe & the earth probe.
• Check for process buildup in the vacuum generator. Clean as necessary. • Check the vent valve and line are clean. A blocked vent will prevent the
sample being dropped into the sample cone. • Check for correct operation of all other valves via the maintenance
switches. • Ensure all connections are tightened correctly with no leaks. • With sampler still in Local, switch off the Maintenance mode and press
the Local Start button. The sampler will do 1 cycle but does not post any results to the DCS. During this cycle observe operation of sampler and check all components for correct operation.
• If satisfied with the sampler operation return it to continuous operation by placing it back to Remote.