1 Safety Information
The safe operation of the product depends on qualified personnel (see Section 1.11) correctly carrying out installation, commissioning and maintenance in accordance with the operating procedures.
Compliance with general pipeline and plant construction installation and safety instructions, together with the proper use of tools and safety equipment, is essential.
This product is designed and manufactured to withstand a certain amount of external force during normal use. Using this product for any other purpose, or installing it incorrectly because the installation and maintenance instructions were not followed, may damage the product, invalidate its marking or cause personal injury.
Additional Safety Information: Level Control and Level Limit/Alarm Products for Steam Boilers
Products and systems must be selected, installed, operated and tested in accordance with the following:
- Local and national standards and regulations
- Guidance documents, including the Health and Safety Executive guidance BG01 and INDG436 in the UK
- Requirements of the regulatory authorities
- Boiler inspection departments
- Boiler manufacturer’s specifications
Two independent low water level limit/alarm devices must be installed on steam boilers.
Level sensors must be installed in a protection tube/chamber with sufficient clearance between the protection tube and the sensor end, and must be grounded.
Each sensor must be connected to an independent controller. When a low water level alarm occurs, resetting the alarm must shut down the boiler.
The high water level alarm may form part of the level control system or may be an independent system.
For safety reasons, an independent high water level alarm system must be installed. In this case, resetting the alarm at a high water level must shut off the boiler’s feedwater and steam supplies. All boiler water level limit/alarm systems require regular functional testing.
A complete water treatment regime will ensure the continued safe and correct operation of the control and limit/alarm systems. Advice may be obtained from the organizations listed above and from qualified water treatment companies.
Warning
This product complies with the Electromagnetic Compatibility Directive 2004/108/EC and all applicable requirements.
This product is suitable for heavy industrial environments and has undergone a comprehensive and detailed EMC assessment. BH PA420 supplied in the UK has a reference number. Under the following conditions, the product may experience interference when the limits for immunity in heavy industrial environments are exceeded:
- The product or its wiring is located close to radio transmitters.
- Excessive electrical noise is present in the power supply circuit. If this occurs, an AC power protection device should be installed. The device can filter interference, suppress surges and provide lightning protection.
- A mobile telephone or portable radio is used within 1 m (39”) of the product or its wiring. The actual required distance may vary according to the installation environment and the power source of the signal.
If the product is used in a manner not specified in this document, the protection provided may be impaired.
1.1 Intended Use
- Check that the product is suitable for the fluid whose level is to be monitored.
- Check the suitability of the materials and the maximum and minimum pressure and temperature values. If the product’s maximum operating limits are lower than those of the system in which it is to be installed, or if product failure could result in a hazardous overpressure or overtemperature condition, ensure that the system includes safety devices to prevent such conditions.
- Ensure that the installation location and flow direction are correct.
- Spirax Sarco products are not designed to withstand external stresses that may be imposed by any system in which they are installed. It is the installer’s responsibility to anticipate these stresses and take appropriate precautions to minimise them. Spirax Sarco accepts no responsibility in this regard.
- Remove the protective cap from the protective connection before installation.
1.2 Access
Ensure safe access before carrying out any work. If necessary, provide a safe working platform with suitable protection and arrange suitable lifting equipment where required.
1.3 Lighting
Ensure adequate lighting, particularly where detailed or complex work is required.
1.4 Hazardous Liquids or Gases in the Pipeline
Consider the fluids that may be present or may previously have been present in the pipeline. Factors to consider include whether the fluids are flammable, hazardous to health, or subject to temperature limits.
1.5 Hazardous Environments Around the Product
Consider the following: explosive atmospheres, lack of oxygen such as in containers or pits, hazardous gases, extreme temperatures, hot surfaces, fire hazards during welding, excessive noise and moving machinery.
1.6 The System
Consider the effect of the intended work on the entire system. Could any planned action, such as closing isolation valves or disconnecting the power supply, put other parts of the system or personnel at risk?
Hazards may arise from shutting off or closing discharge or protective devices, or from disabling controls or alarms. Isolation valves must be operated slowly to prevent system fluctuations.
1.7 Pressure Systems
Ensure that all pressure has been isolated and safely vented to atmospheric pressure. Consider double isolation and the locking and tagging of closed valves. Do not assume that the system is depressurised even when the pressure gauge indicates zero.
1.8 Temperature
After isolation, allow sufficient time for the equipment to cool to ambient temperature to avoid burns.
1.9 Tools and Spare Parts
Before starting work, ensure that suitable tools and readily replaceable spare parts are available. Use only genuine spare parts supplied by Spirax Sarco.
1.10 Protective Clothing
Consider whether you and nearby personnel require protective clothing to guard against hazards such as chemicals, high or low temperatures, radiation, noise, falling objects, and eye or facial injuries.
1.11 Permits to Work
All work must be carried out or supervised by suitably competent personnel. Installation and maintenance personnel must be trained in the correct operation of the product in accordance with the installation and maintenance instructions.
A formal permit-to-work system must be followed. Where such a system is not available, the person responsible should be informed of the work being carried out and should arrange assistants to be responsible for safety where necessary.
Post warning notices where required.
1.12 Manual Handling
Manual handling of large or heavy items may cause injury. Lifting, pushing, pulling, carrying or supporting loads by hand can cause injury, particularly back injuries. Customers are advised to assess the task, the personnel, the load and the working environment, and to use appropriate handling methods for the circumstances.
1.13 Residual Hazards
Under normal conditions, the external surfaces of the product may be very hot.
Many products are not self-draining. Take extreme care when dismantling the product.
1.14 Freezing
When the product is exposed to temperatures below 0 °C, valves without self-draining capability may be damaged by freezing. Appropriate measures must be taken to protect them.
1.15 Disposal
When disposing of this product, take suitable precautions in accordance with local regulations.
Unless otherwise stated in the installation and maintenance instructions, this product is recyclable and does not present an environmental hazard when disposed of correctly.
1.16 Returning Products
Customers and stockists are reminded that, under EC health, safety and environmental legislation, when returning products to Spirax Sarco, they must provide information about hazards and the precautions to be taken when handling contaminated residues or mechanical damage. Such contamination or damage may present a risk to health, safety or the environment. Written health and safety data must be provided for any substance that is hazardous or potentially hazardous.
2 Product Overview
The PA20 preamplifier is designed for use with Spirax Sarco capacitive sensors. It amplifies the measured capacitance and converts it into a voltage output proportional to the level.
It consists of an austenitic stainless steel body that screws onto the threaded top of the sensor. It is available with a DIN 43650 plug with a Pg 11 cable gland (see Figure 1), or, for the UL version, with a 1/2” NPT cable entry and four separate wires (see Figure 2). The maximum ambient temperature is 70 °C (158 °F), and the minimum ambient temperature is 0 °C (32 °F). The preamplifier can be used in environments with Pollution Degree 3.
Figure 1: Standard model
Figure 2: UL model
3 Installation
Note: The PA20 must not be installed outdoors without additional protection.
The preamplifier may be installed on the capacitive sensor before or after the sensor is installed in the boiler or tank. Before commissioning the controller/transmitter, allow the PA20 to stabilise at its normal operating temperature for at least 15 minutes.
Fit an O-ring at the bottom of the external thread on the capacitive sensor.
Note: Both the sensor and the PA20 are supplied with an O-ring. Fit only one of them.
Install the preamplifier onto the sensor and tighten it by hand.
Warning: Excessive hand tightening or the use of pipe grips will damage the O-ring and may damage the preamplifier.
Figure 3
4 Wiring
4.1 General
All wiring materials and installation methods must comply with BS 6739 - Design and installation of process control instrumentation systems - or the local equivalent standard. For installations in the United States and Canada, the preamplifier wiring must comply with the requirements of the local and National Electrical Code (NEC) or Canadian Electrical Code (CEC), as applicable.
The PA20 requires 15-35 Vdc (15-24 Vdc Class 2 for UL models) and has a maximum current consumption of 10 mA.
The PA20 is compatible with the input voltage of all Spirax Sarco controllers/transmitters.
Use a 3-core, 1 mm² (18-16 AWG) high-temperature screened cable with a maximum length of 100 m (328 ft). Pirelli FP 200 or Delta Crompton Firetuf OHLS is the standard cable for the PA20. Ensure that sufficient cable length is provided to allow the preamplifier to be removed without deforming the equipment or conduit box.
Warning:
- Do not install signal cables near high-voltage cables or switchgear.
- Sensor wiring must not be installed in the same trench or duct as power cables.
- Take anti-static precautions during installation and servicing.
4.2 Screen connections
A ground loop is created if the cable or screen is connected to two grounding points at different voltages. When the guidelines are followed correctly, the screen of the preamplifier or controller is connected to ground at only one point (see Figure 4).
Note: The PA20 ground terminal is a functional ground, not a protective ground.
Protective grounding provides protection against electric shock under fault conditions. Protective grounding is not required for this product.
Functional grounding is used for product operation. In this application, the grounding point (tank/boiler shell) acts as the common connection for the sensor/preamplifier and also helps reduce electrical interference.
- Ensure that the screen is connected to the PA20 ground terminal and the controller common terminal.
- Ensure that the controller common terminal is not grounded internally (all Spirax Sarco boiler control systems are not internally grounded).
- The controller common terminal must be grounded through the PA20.
Warning: Do not ground the common terminal at the controller. Doing so will create a ground loop, which may impair product operation or damage the product.
Figure 4
Warning: Do not ground this end. It must be grounded only through the sensor cable.
Figure 5
4.3 Terminal box
Remove the terminal box by removing the central screw (see Figures 1 and 2).
Note: To provide environmental protection, the PA20 has a square gasket between the terminal box and the preamplifier connector. To maintain the integrity of the environmental protection, the gasket must remain in place when reconnecting the terminal box, and all mating surfaces must be clean and undamaged.
Remove the central screw and detach the hinged cover to access the terminal board.
The terminal board of the standard PA20 can be rotated through 90° to facilitate wiring:
- Remove the retaining screws, hinged cover and terminal box.
- Remove the terminal board and reinstall it in the required orientation.
Note: The terminal board cannot be rotated on UL models.
4.4 Additional wiring information - UL models
The preamplifier is supplied with four 18 AWG, 12” long, colour-coded flying leads. These are cut to equal lengths and connected to a metal terminal box. A section of flexible metal conduit is installed between the preamplifier and terminal box and provides the electrical conduit connection. For this reason, the terminal box has a 1/2” NPT cable entry. An 18-16 AWG screened cable is recommended between the terminal box and controller.
Warning
- The flying leads supplied with the sensor are rated for 221 °F (105 °C) and must not be exposed to temperatures above this rating.
- The conduit and terminal box must not be connected to any other control wiring, as this may cause damage or reduce product performance.
- The terminal board must not be rotated on UL models, as this will damage the internal wiring.
- Take particular care with condensate, which can accumulate in the wiring system. Prevent condensate from accumulating at the sensor wire connection points and in the terminal box. Keep the drain/vent holes clear and uncovered.
- Before applying power to the PA20, disconnect the terminal box connection and verify that 15-35 Vdc is present between pin 1 and the ground terminal.
4.5 Wiring - both models (Figure 5)
| Terminal | Colour | Function |
|---|---|---|
| Terminal 1 | Brown | Power supply |
| Terminal 2 | Red | Output |
| Terminal 3 | Orange | Sensitivity* |
| Ground terminal | Black | Common |
* On UL models, the sensitivity connection is made inside the terminal box. Depending on how the terminals are wired, terminal 3 provides three different sensitivity ranges (see Section 4.6 below).
Figure 6: Top view of terminal board with cover removed (medium sensitivity)
4.6 Sensitivity settings
- High sensitivity: Immersion length up to 500 mm (20”), connect terminals 1 + 3 (total sensor length up to 550 mm)
- Medium sensitivity: Immersion length up to 1050 mm (41”), no connection
- Low sensitivity: Longer immersion lengths, connect terminal 3 + ground terminal
Figure 7: High sensitivity
Figure 8: Medium sensitivity
Figure 9: Low sensitivity
5 Voltage check
Measure the voltage as follows before commissioning the controller:
- Switch on the controller and raise the water level to the highest required measurement level. For a steam boiler, this is generally the top of the gauge glass.
- Measure the DC voltage between terminal 2 (red) and the ground/common terminal (black) of the preamplifier. The voltage should be between 3 and 6 V.
- If the voltage is above 6 V, change the connection of terminal 3 as shown in Figures 7, 8 and 9, and select the next lower sensitivity range.
- If the voltage is below 3 V, select the next higher sensitivity range as shown in the figures.
- Check that the measured voltage is still between 3 and 6 V.
- If the voltage is still above 6 V, select the lowest sensitivity range.
The graph below (Figure 10) shows the voltage that should be present at the preamplifier for a given sensor insertion depth.
The exact voltage depends on how the sensor is installed and its installed length.
Figure 10: Sensor insertion length in mm (inches)
High sensitivity must be selected when the installed sensor length is between 370 and 550 mm. Selecting medium or low sensitivity will cause an “out of range” condition and an alarm.
6 Maintenance
No special maintenance is required.
Boiler water level control and alarms require regular testing and inspection. Refer to other documentation for details of testing Spirax Sarco systems.
