- Email: [email protected]
Monitoring pumps
feature pump monitoring
Monitoring pumps In this article, Cliff Wyatt discusses methods of performance monitoring and protection of industrial pumps, utilizing power sensing techniques that accurately measure electrical power drawn by pump motors. The focus is on products and techniques developed by specialist manufacturer Load Controls Inc of Sturbridge, MA, USA.
T
he use of power sensing techniques in pump performance monitoring is nonintrusive as the sensor only needs to be wired into the pump supply and there are no probes in the fluid to get contaminated or holes to cut in pipes. This ensures that sensor installation can be achieved with minimum downtime and very low cost. We concentrate here on the front end of the process, the ‘sensor’, as it matters not what sophisticated instrumentation or computers are used to process the sensor’s signals; unless the sensor can respond quickly and accurately to changes in whatever process is being monitored then it will not be possible to make sensible process control decisions.
Power transducers & load controls Sensing motor power is an extremely clever way to get feedback about machine, pump or process performance. Monitoring the load on the motor can give you valuable
programmable controllers, recorders or data collection systems.
information since this motor reflects the changes that are taking place as they happen.
The Hall effect is observed when an electric current flows through a conductor in a magnetic field. The magnetic field exerts a transverse force on the moving charge carriers, which tends to push them to one side of the conductor, positive charge carriers moving one way and negative charge carriers the other. This build-up of opposing charges produces a measurable voltage between the two sides of the conductor: the Hall effect.
On a mixer or agitator, for example, as the viscosity increases, it will take more power to stir the mixture. The beginning and end of processes can be detected precisely with ease. In the case of pumps, sensing power allows the detection of overloads, caused by blockages or mechanical problems, and under-load situations such as loss of prime or cavitation. In addition, changes in pump fluid flow conditions are reflected in levels of motor power allowing rapid warning of possible problems.
Electricity, motors and power
A power sensor like the Digital Pump Load Control senses the load and also has display, delay timers and built-in relays to sound alarms, stop the pump, change feed rates, stop the machine, etc.
Nearly all industrial motors are threephase induction motors. The threephase power creates a rotating field in the stator, which ‘induces’ the rotor to rotate. To measure three-phase power:
A ‘Hall effect’ power sensor such as Load Controls’ UPC (Universal Power Cell) can measure these load changes very precisely and send a signal to meters, computers,
P = EI(cosφ)(1.73) where P = power in watts; I = current in each phase (amps); E = voltage phase to phase (V); cosφ = power
No sensitivity for low loads
Power
Amps
Power factor
0.9
Power is linear Equal sensitivity at both low and high loads
0.1
No load
Full load
(a)
No load (b)
Full load
No load
Full load
(c)
Figure 1. Change in (a) power factor, (b) current and (c) power as load is increased.
WORLD PUMPS December 2004
www.worldpumps.com 17
feature pump monitoring Voltage L1
Motor
Voltage from 2 phases
Voltage transformer with 120 V secondary L2
A 120 V voltage signal is taken from two phases with a transformer. The assumption is: the 120 V signal changes in the same ratio as the primary voltage. This 120 V signal typically comes from a control transformer that is also used for other instrument supply purposes.
Current Current from remaining phase L3
COM 5 A 15 A
Chassis L1 L2 GND 120 V AC
Figure 2. Single element wattmeter technique. Power sensing is done by monitoring the voltage between two of the phases and current in the remaining phase.
factor (ranges from 0–1) and 1.73 is the multiplication factor for three phases = √3 (NB: 1 HP = 746 W).
What is the power factor? In an induction motor, the current always lags the voltage. The power factor is the cosine of this angular lag. For a lightly loaded motor, the power factor can be as low as 0.1. You can think of this low power factor as electrical inefficiency. Current is flowing to the motor but it is not doing useful work (power). As the load increases, the power factor improves and is typically 0.9 for a fully loaded motor.
Why monitor power instead of amps? As you start to load a motor, the power factor improves rapidly while the current doesn’t change significantly until the motor reaches maybe 50% of capacity (Figure 1). Power is linear with load and change in load is a change in power (HP or kW). Measuring power gives you the signal that you need for monitoring and
18
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control of pump, machine or process. When the load is low, power is low. When the load is high, power is high. At light loads, power is perhaps ten times more sensitive than amps. We often get calls saying, “I put a clamp-on ammeter on the motor and I’m getting 50% of full load amps. Your device is only reading 10%. What’s going on?” If you look at the curve in Figure 1b, you can see that for a lightly loaded motor the current is high. Why? The power factor is low! As you start to load the motor, the power factor increases, but the current doesn’t change much. This is the advantage of sensing power, which is directly proportional to load, rather than amps.
Two ways to measure power Single element wattmeter In many of the Load Controls units, the single element wattmeter technique for sensing power is used (Figure 2).
The current signal is taken from the remaining phase with a current sensing toroid that is either built into the control or located extern-ally. For large motors a current transformer is used together with the toroid.
Power factor The control calculates the power factor by sensing the ‘zero crossing’ of the AC voltage (AC voltage changes from + to – and back) and the zero crossing of the AC current. This lag is the power factor.
Assumption The technique assumes that the load is balanced. Since a load control is normally used on a single motor, the imbalance between phases is small. If more than one motor is being sensed from a single location, use the second method of measuring power, the Power Cell, which measures current and voltage in all three phases. The single element wattmeter technique also doesn’t work well on variable frequency drives (VFDs). If you are using a VFD drive, you need to use a Power Cell.
Power Cell Traditional techniques do not work for measuring the power from a VFD. • Current transformers (and clampon ammeters) do not work at very low or high frequencies. • Voltage transformers do not work at very low or high frequencies. • The wave shape as it leaves the drive is too distorted to use zerocrossing techniques. • Many lower-cost instruments are designed for sine wave calculations of values of current and voltage.
WORLD PUMPS December 2004
feature pump monitoring
The bottom line is that this may be the only sensor that works properly on the output of a drive.
L1
L3
7
Volts L2 Volts L3
Volts L1
pply faces su
4-20 mA output Analog common 0-10 V output Chassis ground 120 VAC 120 VAC
This side
8
9
4 5 6 1 2 3
Using Hall effect devices instead of the traditional CTs and VTs greatly simplifies installation. Accuracy is also improved by eliminating the phase shift errors from CTs and VTs, which can be large at low power factors. The Hall devices will also work on the output of VFDs. The analogue output can be connected to meters, computers, programmable controllers, chart recorders and data loggers. It can also be used together with a ‘V’ series load control if trip points and relay outputs are required.
L1 voltage sample L2 voltage sample L3 voltage sample Single phase or DC L1
L3
MOTOR This side
ply faces sup
7
8
9
4 5 6 1 2 3
L1 voltage sample
L3 voltage sample
Unique Sensor MOTOR
The Power Cell (Figure 3) is a unique power sensor. It uses three balanced Hall effect devices. Hall effect semiconductors have two characteristics: they sense a magnetic field and they can multiply two signals. When a current-carrying conductor passes through a magnetic flux concentrator and the Hall effect sensor is placed in a gap in the concentrator, the signal is proportional to the current. The Hall effect sensor is also excited with a signal that comes from the voltage sample for that phase. The Hall device multiplies these two signals. The resulting output is then
L2
Three phase
Volts L2 Volts L3
The solution is to use the Power Cell, since the Hall effect sensors are not affected by the odd wave shapes and frequency. Also, no current transformers (CTs) and voltage transformers (VTs) are used.
proportional to power (volts x amps). This is an instantaneous vector multiplication, which also calculates the lag or lead of the current (power factor). The signals for each of the three-phases are summed and the analogue output signal is proportional to the three-phase power (HP or kW).
Volts L1
Traditional schemes for measuring the power on the input to the drive are also not reliable. • The drive doesn’t take its power in sine waves. It takes power only during part of the cycle as it is charging capacitors. • The drive often takes power at a high power factor regardless of the motor load. This won’t give a true value for lightly loaded motors.
Pump performance monitoring Although these power monitoring techniques are applicable to most types of industrial pumps, they particularly apply for critical and environmentally sensitive pumping applications where magnetically coupled, ‘seal-less’ or ‘canned’ pumps may be used as they offer a number of clear advantages. With these pumps the bearings are contained inside the pump, requiring the presence of fluid to dissipate and remove the heat build-up. Because
Figure 3. Load Controls' Power Cell Transducer works with three phase, single phase or DC motors.
repair or replacement of this type of pump can be extremely expensive, coupled with possibly serious downtime, effective monitoring systems become an extremely good investment. Monitoring pump power tells you what’s happening to the fluid, as illustrated by Figure 4. Thus, you can see that low power indicates dry running, loss of prime, blocked/closed inlet or cavitation while high power
Pump power
40
Valve closing Pumping 20
Valve opening
No fluid
0
Figure 4. The curve shows the power changes on a centrifugal pump as the outlet valve is closed and opened, and the drop in power when there is no liquid.
WORLD PUMPS December 2004
www.worldpumps.com 19
feature pump monitoring when other power sensors and motor load controls are unable to function reliably. The sensor has both 4–20 mA and 0–10 V analogue outputs and a range of accessories including both analogue and digital power displays and set point trip units.
Figure 6. The range finder toroid is used in the pump load control for the current sample. It has six dipswitches that let you select capacities from small motors up to 50 HP with this single sensor. This simplifies installation and set up. Above 50 HP, it can be used in conjunction with an external current transformer.
Figure 5. The PMP-25 compact Digital Pump Load Control is designed specifically for pump monitoring and control. It measures true power and has a digital load display. Display configurations include % full load, HP or kW.
warns of jammed impellers, bad bearings or mechanical problems.
Digital pump load control The compact PMP-25 Digital Pump Load Control (Figure 5) provides an efficient low-cost solution to the prevention of damage to industrial electric motors caused by overload, jamming, loss of load or pump dry running. The rugged polycarbonate sealed enclosure may be mounted in many configurations including on a door, wall or cabinet or inside the control enclosure. The unit is easy to install and displays true power (volts x amps x power factor). Both high and low power trip relays with adjustable start-up delay and individual trip timers are standard features. The high power trip is provided for the detection of problems such overloads, jammed impellers, bad bearings or blocked
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outlets and a low power trip provides detection of low load or no flow conditions such as cavitation or loss of prime. The low power trip, when used to detect dry running, is up to ten times more sensitive than that of conventional undercurrent relays. The 4–20 mA analogue output and individual trip relays allow the flexibility of pump motor control and performance monitoring via external instruments such as computers. The product is compatible with three-phase motors ranging in size up to 373 kW, operating on supplies between 208 V and up to 575 V. A unique range finder toroid (Figure 6) allows easy range set up, particularly when installing small pump motors. The PMP-25 is suited to a wide range of applications in industry and works extremely well with tasks such as protecting pumps of all types, including seal-less or magnetic drive, centrifugal, positive displacement, process and sewage pumps.
Universal Power Cell The new ‘Universal’ Power Cell (UPC; Figure 7) has been designed specifically for precision process monitoring and control. The product is designed to cope with the most difficult of motor load sensing tasks,
The UPC senses instantaneous power drawn by a pump, which is a good indicator of flow and viscosity, also allowing loss of prime or overload situations to be detected rapidly. These transducers are also fast enough to detect mechanical problems such as bearing break-up and pump vibration, to assist with preventative maintenance. Many pump manufacturers use these devices on calibration rigs to assist with quality control in the final test of their pumps. The device is truly ‘universal’, being designed to cope with three-phase AC, variable frequency, single phase and DC in a single model. It does not use CTs or external VTs and its full scale range may be adjusted by the user with coarse and fine pots to accommodate any motor size up to 120 kW. The UPC is extremely sensitive and accurately measures true electrical power drawn on the input to any industrial pump or electric motordriven machine. It is designed to perform exceptionally well in applications on the ‘output’ of VFDs or inverter drives. Wave shape is likely to be poor in these circumstances or power factors may be very low when the motor is lightly loaded, but this is no problem for the UPC. Conventional CT-based power sensors are not suitable for such conditions and will, if used, produce gross power errors (and thus load errors) due to limitations in bandwidth and sensitivity. Where a VFD is involved and relay set points are required, the UPC can be used in conjunction with a special version of the Digital Pump Load Control (PMP-25-V), making the
WORLD PUMPS December 2004
feature pump monitoring The system uses TCP/IP and UDP Protocol with 10 Base-T 10 megabit ethernet connection. In addition, the sensor has a 0–10 V DC analogue output, which can feed to a local monitoring display to assist with troubleshooting. The UPC-E motor load sensor can monitor both fixed and variable frequency power. It also works on single phase, DC and brushless DC. Just as the standard UPC, it has three balanced Hall effect sensors, each with a flux concentrator. The Hall effect semiconductor does a vector multiplication of the current flow and voltage, which also calculates the power factor. The output is proportional to power (HP or kW).
Figure 7. The ‘Universal’ Power Cell for difficult load-sensing tasks.
most of the features of this product, including the timers and display.
Portable Power Cell Load Controls’ new PPC-3 portable power cell (Figure 8) offers accurate and extremely fast (15 ms) true power measurement ideal for machine and pump analysis or process development, allowing process engineers the flexibility to assess the performance of individual machines and product processes. The instrument has been designed to complement the range of Power Cell transducers for process control. Using three clip-on Hall effect current sensors, the instrument has a wide frequency response, is not affected by poor wave shape or frequency and is suitable for use on the output of VFD or inverter drives. Many other power monitors use CTs and cannot provide accurate measurements under such conditions. The power monitor is mounted in a rugged, portable waterproof case. The display features peak emphasis allowing fast-moving events to be monitored. Selection switches provide flexible ranges and both 0–10 V and 4–20 mA isolated analogue outputs allow measurements to be transferred to remote instrumentation.
WORLD PUMPS December 2004
Monitoring pumps with ethernet A new approach to remotely monitoring pumps and machine motors is by using Load Controls’ new Ethernet Universal Power Cell (UPC-E). The use of ethernet has many advantages. A large city in the USA is currently evaluating this new concept and is considering the new UPC-E for monitoring pumps, citywide, over the internet. The UPC-E has a built in web server. An IP address identifies a given sensor on a network, providing access to its home page and links within its ‘site’ to make scaling adjustments and set up UDP (machine code) outputs through a port to a specific machine or to all machines that listen on that port.
In some cases, the average power signal may be more useful than instantaneous power. The Response Adjustment slows the response of the Universal Power Cell. Adjustment is made via the ethernet connection. ■ CONTACT Cliff Wyatt Vydas International Marketing Swan House, Passfield Business Centre Lynchborough Road, Passfield, GU30 7SB, UK. Tel: +44-1428-751822 Fax: +44-1428-751833 E-mail: [email protected] www.vydas.co.uk
The versatility of the UPC combined with ethernet control and communication-embedded web server allows you to change settings on the fly during a machine or process cycle via your browser; for example: • Set full-scale HP/kW to match the motor • Set response time to average the load for a smooth signal • Choose how often to receive data • Or, respond to UDP or HTTP request.
Figure 8. ‘Suitcase’ portability is often a requirement for hardpressed engineers who need to monitor and maintain pumps and motors. Load Controls’ PPC-3 ensures rapid connection with ‘Hall effect’ current clamps and voltage clips plus built-in displays and analogue outputs.
www.worldpumps.com 21
Monitoring pumps In this article, Cliff Wyatt discusses methods of performance monitoring and protection of industrial pumps, utilizing power sensing techniques that accurately measure electrical power drawn by pump motors. The focus is on products and techniques developed by specialist manufacturer Load Controls Inc of Sturbridge, MA, USA.
T
he use of power sensing techniques in pump performance monitoring is nonintrusive as the sensor only needs to be wired into the pump supply and there are no probes in the fluid to get contaminated or holes to cut in pipes. This ensures that sensor installation can be achieved with minimum downtime and very low cost. We concentrate here on the front end of the process, the ‘sensor’, as it matters not what sophisticated instrumentation or computers are used to process the sensor’s signals; unless the sensor can respond quickly and accurately to changes in whatever process is being monitored then it will not be possible to make sensible process control decisions.
Power transducers & load controls Sensing motor power is an extremely clever way to get feedback about machine, pump or process performance. Monitoring the load on the motor can give you valuable
programmable controllers, recorders or data collection systems.
information since this motor reflects the changes that are taking place as they happen.
The Hall effect is observed when an electric current flows through a conductor in a magnetic field. The magnetic field exerts a transverse force on the moving charge carriers, which tends to push them to one side of the conductor, positive charge carriers moving one way and negative charge carriers the other. This build-up of opposing charges produces a measurable voltage between the two sides of the conductor: the Hall effect.
On a mixer or agitator, for example, as the viscosity increases, it will take more power to stir the mixture. The beginning and end of processes can be detected precisely with ease. In the case of pumps, sensing power allows the detection of overloads, caused by blockages or mechanical problems, and under-load situations such as loss of prime or cavitation. In addition, changes in pump fluid flow conditions are reflected in levels of motor power allowing rapid warning of possible problems.
Electricity, motors and power
A power sensor like the Digital Pump Load Control senses the load and also has display, delay timers and built-in relays to sound alarms, stop the pump, change feed rates, stop the machine, etc.
Nearly all industrial motors are threephase induction motors. The threephase power creates a rotating field in the stator, which ‘induces’ the rotor to rotate. To measure three-phase power:
A ‘Hall effect’ power sensor such as Load Controls’ UPC (Universal Power Cell) can measure these load changes very precisely and send a signal to meters, computers,
P = EI(cosφ)(1.73) where P = power in watts; I = current in each phase (amps); E = voltage phase to phase (V); cosφ = power
No sensitivity for low loads
Power
Amps
Power factor
0.9
Power is linear Equal sensitivity at both low and high loads
0.1
No load
Full load
(a)
No load (b)
Full load
No load
Full load
(c)
Figure 1. Change in (a) power factor, (b) current and (c) power as load is increased.
WORLD PUMPS December 2004
www.worldpumps.com 17
feature pump monitoring Voltage L1
Motor
Voltage from 2 phases
Voltage transformer with 120 V secondary L2
A 120 V voltage signal is taken from two phases with a transformer. The assumption is: the 120 V signal changes in the same ratio as the primary voltage. This 120 V signal typically comes from a control transformer that is also used for other instrument supply purposes.
Current Current from remaining phase L3
COM 5 A 15 A
Chassis L1 L2 GND 120 V AC
Figure 2. Single element wattmeter technique. Power sensing is done by monitoring the voltage between two of the phases and current in the remaining phase.
factor (ranges from 0–1) and 1.73 is the multiplication factor for three phases = √3 (NB: 1 HP = 746 W).
What is the power factor? In an induction motor, the current always lags the voltage. The power factor is the cosine of this angular lag. For a lightly loaded motor, the power factor can be as low as 0.1. You can think of this low power factor as electrical inefficiency. Current is flowing to the motor but it is not doing useful work (power). As the load increases, the power factor improves and is typically 0.9 for a fully loaded motor.
Why monitor power instead of amps? As you start to load a motor, the power factor improves rapidly while the current doesn’t change significantly until the motor reaches maybe 50% of capacity (Figure 1). Power is linear with load and change in load is a change in power (HP or kW). Measuring power gives you the signal that you need for monitoring and
18
www.worldpumps.com
control of pump, machine or process. When the load is low, power is low. When the load is high, power is high. At light loads, power is perhaps ten times more sensitive than amps. We often get calls saying, “I put a clamp-on ammeter on the motor and I’m getting 50% of full load amps. Your device is only reading 10%. What’s going on?” If you look at the curve in Figure 1b, you can see that for a lightly loaded motor the current is high. Why? The power factor is low! As you start to load the motor, the power factor increases, but the current doesn’t change much. This is the advantage of sensing power, which is directly proportional to load, rather than amps.
Two ways to measure power Single element wattmeter In many of the Load Controls units, the single element wattmeter technique for sensing power is used (Figure 2).
The current signal is taken from the remaining phase with a current sensing toroid that is either built into the control or located extern-ally. For large motors a current transformer is used together with the toroid.
Power factor The control calculates the power factor by sensing the ‘zero crossing’ of the AC voltage (AC voltage changes from + to – and back) and the zero crossing of the AC current. This lag is the power factor.
Assumption The technique assumes that the load is balanced. Since a load control is normally used on a single motor, the imbalance between phases is small. If more than one motor is being sensed from a single location, use the second method of measuring power, the Power Cell, which measures current and voltage in all three phases. The single element wattmeter technique also doesn’t work well on variable frequency drives (VFDs). If you are using a VFD drive, you need to use a Power Cell.
Power Cell Traditional techniques do not work for measuring the power from a VFD. • Current transformers (and clampon ammeters) do not work at very low or high frequencies. • Voltage transformers do not work at very low or high frequencies. • The wave shape as it leaves the drive is too distorted to use zerocrossing techniques. • Many lower-cost instruments are designed for sine wave calculations of values of current and voltage.
WORLD PUMPS December 2004
feature pump monitoring
The bottom line is that this may be the only sensor that works properly on the output of a drive.
L1
L3
7
Volts L2 Volts L3
Volts L1
pply faces su
4-20 mA output Analog common 0-10 V output Chassis ground 120 VAC 120 VAC
This side
8
9
4 5 6 1 2 3
Using Hall effect devices instead of the traditional CTs and VTs greatly simplifies installation. Accuracy is also improved by eliminating the phase shift errors from CTs and VTs, which can be large at low power factors. The Hall devices will also work on the output of VFDs. The analogue output can be connected to meters, computers, programmable controllers, chart recorders and data loggers. It can also be used together with a ‘V’ series load control if trip points and relay outputs are required.
L1 voltage sample L2 voltage sample L3 voltage sample Single phase or DC L1
L3
MOTOR This side
ply faces sup
7
8
9
4 5 6 1 2 3
L1 voltage sample
L3 voltage sample
Unique Sensor MOTOR
The Power Cell (Figure 3) is a unique power sensor. It uses three balanced Hall effect devices. Hall effect semiconductors have two characteristics: they sense a magnetic field and they can multiply two signals. When a current-carrying conductor passes through a magnetic flux concentrator and the Hall effect sensor is placed in a gap in the concentrator, the signal is proportional to the current. The Hall effect sensor is also excited with a signal that comes from the voltage sample for that phase. The Hall device multiplies these two signals. The resulting output is then
L2
Three phase
Volts L2 Volts L3
The solution is to use the Power Cell, since the Hall effect sensors are not affected by the odd wave shapes and frequency. Also, no current transformers (CTs) and voltage transformers (VTs) are used.
proportional to power (volts x amps). This is an instantaneous vector multiplication, which also calculates the lag or lead of the current (power factor). The signals for each of the three-phases are summed and the analogue output signal is proportional to the three-phase power (HP or kW).
Volts L1
Traditional schemes for measuring the power on the input to the drive are also not reliable. • The drive doesn’t take its power in sine waves. It takes power only during part of the cycle as it is charging capacitors. • The drive often takes power at a high power factor regardless of the motor load. This won’t give a true value for lightly loaded motors.
Pump performance monitoring Although these power monitoring techniques are applicable to most types of industrial pumps, they particularly apply for critical and environmentally sensitive pumping applications where magnetically coupled, ‘seal-less’ or ‘canned’ pumps may be used as they offer a number of clear advantages. With these pumps the bearings are contained inside the pump, requiring the presence of fluid to dissipate and remove the heat build-up. Because
Figure 3. Load Controls' Power Cell Transducer works with three phase, single phase or DC motors.
repair or replacement of this type of pump can be extremely expensive, coupled with possibly serious downtime, effective monitoring systems become an extremely good investment. Monitoring pump power tells you what’s happening to the fluid, as illustrated by Figure 4. Thus, you can see that low power indicates dry running, loss of prime, blocked/closed inlet or cavitation while high power
Pump power
40
Valve closing Pumping 20
Valve opening
No fluid
0
Figure 4. The curve shows the power changes on a centrifugal pump as the outlet valve is closed and opened, and the drop in power when there is no liquid.
WORLD PUMPS December 2004
www.worldpumps.com 19
feature pump monitoring when other power sensors and motor load controls are unable to function reliably. The sensor has both 4–20 mA and 0–10 V analogue outputs and a range of accessories including both analogue and digital power displays and set point trip units.
Figure 6. The range finder toroid is used in the pump load control for the current sample. It has six dipswitches that let you select capacities from small motors up to 50 HP with this single sensor. This simplifies installation and set up. Above 50 HP, it can be used in conjunction with an external current transformer.
Figure 5. The PMP-25 compact Digital Pump Load Control is designed specifically for pump monitoring and control. It measures true power and has a digital load display. Display configurations include % full load, HP or kW.
warns of jammed impellers, bad bearings or mechanical problems.
Digital pump load control The compact PMP-25 Digital Pump Load Control (Figure 5) provides an efficient low-cost solution to the prevention of damage to industrial electric motors caused by overload, jamming, loss of load or pump dry running. The rugged polycarbonate sealed enclosure may be mounted in many configurations including on a door, wall or cabinet or inside the control enclosure. The unit is easy to install and displays true power (volts x amps x power factor). Both high and low power trip relays with adjustable start-up delay and individual trip timers are standard features. The high power trip is provided for the detection of problems such overloads, jammed impellers, bad bearings or blocked
20
www.worldpumps.com
outlets and a low power trip provides detection of low load or no flow conditions such as cavitation or loss of prime. The low power trip, when used to detect dry running, is up to ten times more sensitive than that of conventional undercurrent relays. The 4–20 mA analogue output and individual trip relays allow the flexibility of pump motor control and performance monitoring via external instruments such as computers. The product is compatible with three-phase motors ranging in size up to 373 kW, operating on supplies between 208 V and up to 575 V. A unique range finder toroid (Figure 6) allows easy range set up, particularly when installing small pump motors. The PMP-25 is suited to a wide range of applications in industry and works extremely well with tasks such as protecting pumps of all types, including seal-less or magnetic drive, centrifugal, positive displacement, process and sewage pumps.
Universal Power Cell The new ‘Universal’ Power Cell (UPC; Figure 7) has been designed specifically for precision process monitoring and control. The product is designed to cope with the most difficult of motor load sensing tasks,
The UPC senses instantaneous power drawn by a pump, which is a good indicator of flow and viscosity, also allowing loss of prime or overload situations to be detected rapidly. These transducers are also fast enough to detect mechanical problems such as bearing break-up and pump vibration, to assist with preventative maintenance. Many pump manufacturers use these devices on calibration rigs to assist with quality control in the final test of their pumps. The device is truly ‘universal’, being designed to cope with three-phase AC, variable frequency, single phase and DC in a single model. It does not use CTs or external VTs and its full scale range may be adjusted by the user with coarse and fine pots to accommodate any motor size up to 120 kW. The UPC is extremely sensitive and accurately measures true electrical power drawn on the input to any industrial pump or electric motordriven machine. It is designed to perform exceptionally well in applications on the ‘output’ of VFDs or inverter drives. Wave shape is likely to be poor in these circumstances or power factors may be very low when the motor is lightly loaded, but this is no problem for the UPC. Conventional CT-based power sensors are not suitable for such conditions and will, if used, produce gross power errors (and thus load errors) due to limitations in bandwidth and sensitivity. Where a VFD is involved and relay set points are required, the UPC can be used in conjunction with a special version of the Digital Pump Load Control (PMP-25-V), making the
WORLD PUMPS December 2004
feature pump monitoring The system uses TCP/IP and UDP Protocol with 10 Base-T 10 megabit ethernet connection. In addition, the sensor has a 0–10 V DC analogue output, which can feed to a local monitoring display to assist with troubleshooting. The UPC-E motor load sensor can monitor both fixed and variable frequency power. It also works on single phase, DC and brushless DC. Just as the standard UPC, it has three balanced Hall effect sensors, each with a flux concentrator. The Hall effect semiconductor does a vector multiplication of the current flow and voltage, which also calculates the power factor. The output is proportional to power (HP or kW).
Figure 7. The ‘Universal’ Power Cell for difficult load-sensing tasks.
most of the features of this product, including the timers and display.
Portable Power Cell Load Controls’ new PPC-3 portable power cell (Figure 8) offers accurate and extremely fast (15 ms) true power measurement ideal for machine and pump analysis or process development, allowing process engineers the flexibility to assess the performance of individual machines and product processes. The instrument has been designed to complement the range of Power Cell transducers for process control. Using three clip-on Hall effect current sensors, the instrument has a wide frequency response, is not affected by poor wave shape or frequency and is suitable for use on the output of VFD or inverter drives. Many other power monitors use CTs and cannot provide accurate measurements under such conditions. The power monitor is mounted in a rugged, portable waterproof case. The display features peak emphasis allowing fast-moving events to be monitored. Selection switches provide flexible ranges and both 0–10 V and 4–20 mA isolated analogue outputs allow measurements to be transferred to remote instrumentation.
WORLD PUMPS December 2004
Monitoring pumps with ethernet A new approach to remotely monitoring pumps and machine motors is by using Load Controls’ new Ethernet Universal Power Cell (UPC-E). The use of ethernet has many advantages. A large city in the USA is currently evaluating this new concept and is considering the new UPC-E for monitoring pumps, citywide, over the internet. The UPC-E has a built in web server. An IP address identifies a given sensor on a network, providing access to its home page and links within its ‘site’ to make scaling adjustments and set up UDP (machine code) outputs through a port to a specific machine or to all machines that listen on that port.
In some cases, the average power signal may be more useful than instantaneous power. The Response Adjustment slows the response of the Universal Power Cell. Adjustment is made via the ethernet connection. ■ CONTACT Cliff Wyatt Vydas International Marketing Swan House, Passfield Business Centre Lynchborough Road, Passfield, GU30 7SB, UK. Tel: +44-1428-751822 Fax: +44-1428-751833 E-mail: [email protected] www.vydas.co.uk
The versatility of the UPC combined with ethernet control and communication-embedded web server allows you to change settings on the fly during a machine or process cycle via your browser; for example: • Set full-scale HP/kW to match the motor • Set response time to average the load for a smooth signal • Choose how often to receive data • Or, respond to UDP or HTTP request.
Figure 8. ‘Suitcase’ portability is often a requirement for hardpressed engineers who need to monitor and maintain pumps and motors. Load Controls’ PPC-3 ensures rapid connection with ‘Hall effect’ current clamps and voltage clips plus built-in displays and analogue outputs.
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