Robertshaw Level Controls work on the Capacitance principle (with the exception of the Model 352 which works on the Conductivity principle). The capacitance probe serves as one plate of the capacitor and the metal vessel wall forms the second plate of the capacitor (reference). If the vessel is non-metal, the second plate is formed by using another form of metal ground reference -- ground rod, concentric shielded probe, ground wire wrapped probe, etc. -- depending on the application requirements. In a non-conductive process, the process itself is the insulating medium (dielectric) between the two plates. In a conductive process, the probe insulation is the insulating medium (dielectric) between the two plates.

As the process level changes, it causes a “capacitance” signal to be generated by the level probe. The instrument acts upon this capacitance signal by providing an output or signal proportional to the process level change. For a simple parallel capacitor, the amount of capacitance generated is directly proportional to the area of the plates and the dielectric constant of the process material, and inversely proportional to the distance between the plates. Since the area of the measuring probe and the distance between the probe and vessel wall or ground reference are fixed (except for proximity measurement), the capacitance change is due to the dielectric change that results from the process level increasing or decreasing, thereby changing the amount of air surrouding the probe.

In the case of proximity measurement, the distance between the plates changes as the process rises toward the probe, with the conductive process being one plate of the capacitor. In this case, the capacitance changes due to the increase or decrease of probe area in contact with the process.

Robertshaw Instruments can be used to measure most liquid materials. See RF Level Controls Selection Guide for direction on how to select the proper instrument and probe to match specific application requirements. Robertshaw Level Controls should not be used for continuous level measurement if the process dielectric/conductivity changes.

Robertshaw Level Instruments can be used to measure most solids or granular materials provided the moisture content does not change, the material is not excessively abrasive, and excessive side loading does not occur, which would damage the probe. See RF Level Controls Selection Guide for further details.

No. Each instrument has it’s own minimum and maximum pF(pico-farad) span that must be met. This pF signal is generated by the particular type of probe, geometry of the installation and dielectric of the process variable being measured. Once a probe is selected for use, it must then be matched to an instrument that will handle the pF span that will be generated. A calculation should be done to insure the minimum and maximum instrument span is met. This calculation must include the Terminal Capacitance Value (see Question 5 - "What is Terminal Capacitance?" in this section). See RF Level Controls Selection Guide for further details.

Terminal Capacitance is the MINIMUM amount of capacitance present when NO product is present in the vessel. This is (1) The capacitance of the probe gland (and sheath and cooling extension, if used) PLUS (2) The capacitance of the coaxial cable when remote mounting the instrument (not applicable for the Model 158A or 310) PLUS (3) The capacitance generated between the probe and the vessel with AIR as the dielectric.

In other words, it is the absolute minimum value of capacitance generated in that particular probe/vessel installation with the vessel empty. See RF Level Controls Selection Guide for further details.

Fail safe modes protect the process and/or environment in the event of a power failure. High Level Fail Safe means the unit provides high level alarm protection in the event of a power failure. For example, if a power failure occurs, the relays trip to the high alarm condition to stop a filling operation. Low Level Fail Safe means the unit provides low level alarm protection in the event of a power failure. For example, if a power failure occurs, the relays trip to the low alarm state to stop an emptying operation.

For on/off applications, this is the distance, in pico-farads or inches or feet, from ZERO to the point at which “reset” is to occur. A “Pump ON" to "Pump OFF" application is a typical case in which differential adjustment can be used.

Yes, but a Ground Reference must be supplied. This can be achieved by installing a ground rod, concentric shielded probe (free flowing liquids only), ground wire probe, or an attachment to a metal object in the tank. The type of grounding must be appropriately selected for a particular application. All types will not work for all applications. See RF Level Controls Selection Guide for further instruction.

Intrinsic Safety refers to a protection concept in which the available energy in an electrical circuit in a hazardous (classified) area is limited to below that which is capable of igniting the most flammable or combustible mixture in that area. An Explosion-Proof enclosure can also be used for protection in the same type of area. This type of protection will contain any explosion without incurring any damage to the enclosure, and prevent ignition of the explosive atmosphere outside the enclosure. If the area in which the level instrument/probe is located is rated/classified hazardous, then the instrument and probe must be rated I.S. or Explosion-Proof for that particular area. Additionally, safety barrier(s) may be required. A General Purpose Instrument CANNOT be used. See Agency Approvals for Robertshaw Level Instruments that are rated I.S. or Explosion-Proof.

For on/off applications, Zero is the "set point" – the point where the desired actuation or alarm is to occur. For continuous level measurement, Zero is the 0% level point on the sensing probe.

Span Adjustment is for continuous level measurement. This is the distance in pico-farads from the Zero level point to the Full or highest desired level measurement point.

This can be achieved by installing a ground rod, concentric shielded probe (free flowing liquids only), ground wire probe, or an attachment to a metal object in the tank. The type of grounding must be appropriately selected for a particular application. All types will not work for all applications. See RF Level Controls Selection Guide for further instructions.

One(1), provided the instrument has differential adjustment (see Question 7). You can use Zero or a set point for pump-ON, and the differential adjustment for pump-OFF.

Yes, for most applications. Low dielectric/non-conductive processes that leave a reasonable amount of coating on the probe do not significantly affect the measurement and do not require anti-coating circuitry. With high dielectric/conductive processes, however, you must select an appropriate probe and instrument that has anti-coating capability. Also, there is a limit to the amount and type of coating that can be ignored – periodic cleaning may be necessary. In some cases, a non-contact technology may be required. In addition, some conductive coatings may be barely visible – such as caustic solutions – which require an anti-coating probe/instrument. If in doubt, consult one of our representatives.

Yes, within reason. The process must drain off the probe in order for a level/capacitance change to take place. A reasonable amount of coating can be error compensated by using anti-coating probes/instruments. In such cases, periodic cleaning may be necessary. In extreme cases, a non-contact technology may be required. If in doubt, consult one of our representatives.

20 ft.

For measurement longer than 20 ft., you must use the Robertshaw flexible probe (Model 729A) – lengths are available up to 100 feet.

This depends on the application:

An insulated probe can be used for any process measurement. You must use an insulated probe for continuous level or point level measurement, with differential adjustment, in high dielectric/conductive processes.

Caution must be used when using a bare probe. A bare probe can be used for continuous level or point level measurement, with or without differential, in low dielectric/non-conductive processes -- provided condensate does not form on the probe, which could potentially short it out.

A bare probe can also be used for point level measurement, without differential, in high dielectric/conductive processes -- again, provided condensate does not form on the probe. (Please note that in this last type of process, the probe will be tip sensitive in vertical mount cases, and trip at or near the probe in horizontal mount cases.)

When in doubt, use an INSULATED PROBE.

This depends on the application. For continuous level or point level with differential measurement, the probe must be mounted vertical.

For point level only (no differential), the probe can be mounted horizontal or vertical. If the probe is mounted vertical in these cases, set point adjustment will not be possible when used in a conductive process (it will be tip sensitive).

Select the probe rated for the temperature and pressure applicable for your particular application. See the RF Level Controls Selection Guide Matrix for pressure and temperature ratings of probes AND the appropriate corresponding instruments. In addition to probe considerations, you must also be concerned about the electronic instrument itself.

For high temperature applications, you will need to choose a remote mounted instrument, or use a Cooling Extension on the Probe.

Yes, it is possible, but the most accurate method is to calibrate to the actual process level. The alternative is to disconnect the probe and insert a capacitance signal into the instrument. This will require fixed capacitors or a pico-farad signal generator. The capacitance input must be calculated based on the dielectric of the process, geometry of the vessel, probe being used and mounting configuration. The Terminal Capacitance (see Question 5) must also be used for calculations. See example in the RF Level Controls Selection Guide.

For measurement of continuous level or point level with differential adjustment, you must change the process level unless you use the alternative calibration method. This alternative calibration method involves disconnecting the probe and inserting a capacitance signal into the instrument. This will require fixed capacitors or a pico-farad signal generator. The capacitance input must be calculated based on the dielectric of the process, geometry of the vessel, probe being used and mounting configuration. The Terminal Capacitance (see Question 5) must also be used for calculations. See example in the RF Level Controls Selection Guide.

For point level measurement without differential, you must raise the level to the desired set point for calibration, unless you use our Model 5100. The Model 5100 has a special feature that allows you to calibrate the high level with the tank empty or below the desired trip point, or calibrate the low level with the tank full or above the desired trip point. This is a very useful feature in many applications.

Yes, using the Model Excalibur 7000. This instrument has built in software to calculate volume. All you need to do is enter (using the keypad or HART Calibrator option) the vessel parameters/dimensions.

Yes, using the Model Excalibur 7000. This instrument has built in software to calculate flow. All you need to do is enter (using the keypad or HART Calibrator option) the flume or weir parameters.

A concentric shield on a probe can be used to: (1) Increase the gain of the probe in low dielectric/non-conductive liquid products; (2) Linearize a liquid level signal in a horizontal or non-cylindrical vessel; (3) Provide a ground reference in the process liquid of a non-metal or insulated tank. A concentric shield can only be used in free-running, water-like liquid products. A concentric shield is always the same length as the overall probe length.

A sheath on a probe is used to deaden the upper portion of a probe. A sheath should always be used when inserting a probe through a stand-pipe or nozzle in order to negate unwanted capacitance changes resulting from condensate. Otherwise, significant measurement errors will occur. A sheath can also be used to deaden the upper portion of a probe that is not being used for level measurement (above the 100% span point or above the point level set point); this will eliminate the errors typically caused by condensate or changing air/vapor conditions. A sheath is always shorter than the overall length of the probe.

Follow the guidelines in the RF Level Controls Selection Guide. If you need additional help, contact the Robertshaw Representative for your area. They will be happy to provide you with application assistance as well as pricing and delivery details.

Robertshaw offers a variety of actuator sizes and options, along with a broad selection of valves: in numerous sizes with up to 6 in. ports; with direct-, reverse-, or three-way action; and available in brass, steel, and stainless steel. This wide variety of options allows you to select a regulator and valve that closely fit your application, and offer years of satisfactory service. To select the most appropriate regulator and valve to fit your needs, begin by answering the following questions, and then consulting the Control Valve Selection Guide or contacting your local sales representative:

a. What is the process? (steam, water, other)
b. Is the application for "heating" or "cooling"?
c. What temperature do I want to maintain?
d. What is the maximum flow required?

Probably the most important part of selecting the proper regulator is sizing the valve. Undersized, the valve will not yield enough flow. Oversized, it will not give proper control. To select the correct valve size:

a. Find the Cv (the engineering sizing coefficient) of the valve. Using the information of pressure drop, flow, viscosity, specific gravity, etc., calculate the required Cv using a formula, sizing program, or the Robertshaw "Flo-Rule". (Cv=gpm of water at 1 psi pressure drop)
b. Choose the proper valve according to the product specifications, or reference the Control Valve Selection Guide.
c. A valve sizing "Rule-of-Thumb": For proper control, a valve should be one to two sizes smaller than the pipe to which it is being fitted.

For standard temperature regulators (RT1001, RT1003, etc.), when the charge is lost in the thermal system the spring in the actuator will force the valve stem into the up position, fully opening a direct-acting (heating) valve or closing a reverse-acting (cooling) valve. For the RT1006B1 and RT1007A1 Series, however, the failure mode is the opposite.

Yes. In the event of a loss of charge, the RT1006B1 & RT1007A1 Series are designed to automatically move the actuator stem down, closing a direct acting (heating) valve or opening a reverse-acting (cooling) valve.

Although not “fail safe”, the RT1009 and RT1010A Series offer a handcrank option to manually position the valve. In case of thermal system failure, the operator can manually position the valve to the “safe” mode.

Robertshaw sells field replacement assemblies for temperature regulators, as opposed to "spare parts". Generally, Robertshaw regulators lasts up to 30 years before needing replacement parts. When damage or failures does occur, however, we offer the following replacement options:

a. Thermal Assembly: bulb, capillary, cup & bellows
b. Complete upper works: includes thermal assembly, frame and spring
c. Valve Assembly
d. Valve Repair Kit

Robertshaw offers a selection of temperature regulator models based on four different technology options: vapor-pressure, solid-liquid filled, hot chamber and power pill actuated. Vapor-pressure models are the most widely used because of their expanded application limits. Some of the different temperature regulator models available are listed below:

a. Vapor-pressure: RT921 through RT1011 (heating, cooling, mixing/diverting)
b. Solid-Liquid Fill: 908-A (cooling water regulator)
c. Hot Chamber: RT-200 Series (steam heating)
d. Power Pill: I-1284/I-1285 (3-way)

Robertshaw regulators are designed to operate within the temperature limits stated on the nameplate, and the valve is designed to close tightly against the line pressure specified/ordered. If the regulator has been operating satisfactorily for some time and trouble develops, the following information may be of assistance:

HEATING
If no heat or inadequate heat is obtained even at the highest temperature setting, check to make sure that the hand valves in front of the regulating valve are open, and that steam of sufficient pressure is passing to the regulator valve. Blow, or otherwise clean, the line strainers. Clean all traps and see that they are in working order. If the return line to the trap is cool, the steam coils may be clogged.

In all cases, the packing nut should only be finger-tight, and the valve stem must be free to move up-and-down without excessive friction.

The usual cause for overheating is the accumulation of scale or other foreign matter on the valve seat(s). Such matter may hold the poppet off-seat, and may eventually cause the seat or poppet to become scored. Slightly scored seats or poppets may be re-ground, but if too badly damaged, a valve replacement or repair kit should be ordered.

Overheating may also be caused by failure of the thermostatic unit.

COOLING
If a regulator is being used for cooling purposes (such as controlling circulation of water or brine) and sufficient cooling is not being obtained, check to make sure that proper circulation through the circuit is not hindered. All lines, strainers, hand valves and passages in heat exchanger should be open. If over-cooling is experienced, scale or other foreign matter may be preventing the poppet from seating, therefore causing excessive flow of the cooling medium.

In all cases, the packing nut should only be finger-tight, and the valve stem must be free to move up-and-down without excessive friction.

Regulators controlling the circulation of brine should be inspected for frost on the valve stem and for a possibly frozen stem in the packing gland.

Control Valves are among the most common final control elements in a classic control loop. A control valve is a variable orifice or restriction device that can be installed in piping.

Robertshaw Control Valves are diaphragm actuated pneumatic control valves with globe style bodies.

The multi-spring actuator styles VC230A/VC231A are very versatile 30 - sq. in. diaphragm actuators. They are offered in direct- or reverse-acting styles and are field reversible. They can accommodate a variety of valve assemblies ranging from narrow reduced port styles to 6 in. 3-way styles.

The 10 - sq. in. Model VC-210 is also quite versatile and is bellows sealed. It is available with direct-, reverse-, or 3-way action, and in brass or stainless steel constructions.

Generally, our valves are used for control in light industrial applications such as low-pressure steam, water, or air. A great number of applications exist for virtually any type of wet process including pigment & dye machinery, commercial buildings, natural gas pipelines, food & beverage, etc.

Each of the following needs to be considered separately for proper selection:
a. Materials of construction: brass, stainless steel, steel, other
b. Style: 2-way, 3-way, class of shut off, number of ports, etc.
c. Characteristics: quick opening, linear, equal percentage
d. Size: size of connecting pipe, Cv (the engineering size coefficient) necessary to meet flow requirements
e. Actuator: size, action
f. Accessory equipment: positioner, I-P transducer, solenoid, etc.

See Control Valve Selection Guide for further details

Robertshaw diaphragm actuated control valves are designed to control the flow of a fluid passing through a valve by responding to a pneumatic signal from an instrument or pilot controller. The opening, closing and throttling action of the valve is controlled by changes in the instrument output pressure as it responds to changes in the system being controlled.

Size is probably the most critical element in valve selection. Undersized, a valve will not yield enough flow. Oversized, it will not give proper control. To select the correct valve size:

a. Find the Cv (the engineering sizing coefficient) of the valve. Using the information of pressure drop, flow, viscosity, specific gravity, etc., calculate the required Cv using a formula, sizing program, or the Robertshaw “Flo-Rule”. (Cv=gpm of water at 1 psi pressure drop)
b. Choose the proper valve according to the product specifications, or reference the Control Valve Selection Guide.
c. A valve sizing “Rule-of-Thumb”: For proper control, a valve should be one to two sizes smaller than the pipe to which it is being fitted.

Incorporate a Robertshaw Self-Actuated Temperature Regulator into your system. Another quick and easy method to design a temperature control loop is to install a Robertshaw DT-700 Fultrol Pilot Temperature Controller and a VC-210 Control Valve. Both units are normally carried in stock and available for immediate shipment.

Vibration is the mechanical motion of a machine or part back-and-forth from its point of equilibrium. More specifically, we define vibration as: a condition indicating impending danger on an operating machine when the "vibration" appears to be exceeding a level previously considered normal. Note the clause, "a level previously considered normal". During operation, all machines incur some amount of normal or inherent vibration. For example, an automobile engine, in perfect condition and tune, does have some level of inherent vibration. When it starts to run "roughly", however, the vibration level increases. This is the type of "vibration" Robertshaw Vibration Controls are designed to detect and alert you to, before excessive damage can occur to machinery.

Vibration consists of two basic elements: Displacement (amplitude) and frequency (number of vibrations back-and-forth from a neutral point). Acceleration and velocity are associated with these two elements.

To help you further understand the mechanics of vibration, we will define the these terms:

a. Displacement: Amplitude – the magnitude of movement or motion; total distance traveled from one extreme limit of travel to the opposite extreme limit of travel; peak-to-peak displacement. This is normally expressed in mils (1/1000 of an inch), and is seen in the "bending" of a moving part. The greater the bending/displacement of a moving part, the more likely that part is to fail.

b. Frequency: Number of complete sine waves of motion or movement a machine part will make in one unit of time, normally expressed in "revolutions per minute" or "cycles per second". Thus, increased frequency of movement results in increased bending from displacement, which increases the rate at which a machine or part will fail from excessive vibration.

c. Velocity: The rate of change of displacement with respect to time; speed of movement; the first derivative of displacement with respect to time. Velocity is greatest at the neutral point of a bend/displacement due to the following fact: a machine must come to a complete stop at each extreme limit of its movement before it can change its direction of movement. It will then increase its speed until it reaches its peak at the neutral point, then begin slowing down until it reaches the other extreme point. The neutral point is the point of "Peak Velocity". The magnitude of velocity is proportional to the displacement and the frequency of vibration. Velocity is normally expressed in "inches per second".

d. Acceleration: The rate of change of velocity with time; the second derivative of displacement with respect to time, or the first derivative of velocity with respect to time. Points of maximum acceleration occur at the extreme limits of travel of a moving part – when the part must stop and restart in the opposite direction. Large forces of acceleration can occur at high frequencies even though the displacement and velocity of the vibration are small. Acceleration is a function of displacement and the square of the frequency, expressed in G’s.

As you can see, displacement is just one important parameter to measure. The frequency of vibration is just as important, if not more important. Many machines can have excessive vibration – due to a high frequency of movement – while incurring with very little displacement. Acceleration or Velocity sensor instruments measure BOTH frequency AND displacement. Displacement sensors do not. ALL Robertshaw Vibration Sensors measure ACCELERATION or VELOCITY. As indicated above, the magnitude of acceleration is proportional to displacement and is the square of the frequency. Therefore, doubling the amplitude will double the destructive shock, and doubling the frequency will increase the destructive shock by four times.

e. Sine Wave: The type of vibration produced by a single frequency, such as a musical instrument. Also known as sinusoidal or pure harmonic motion. This type of motion rarely, if ever, occurs on an operating machine. Rather, a machine will exhibit a complex waveform, as described below.

f. Complex Wave: Periodic, non-sinusoidal vibration. Typically, rotating and reciprocating machines will have a basic frequency and numerous harmonics associated with each of their various moving parts. The resultant complex waveform is the sum of the basic frequency and amplitude of the machine in addition to all of the harmonic frequencies and amplitudes of the machine. This sum reveals the total destructive force acting on the machine. All Robertshaw Vibration Instruments measure the total vibration resulting from all amplitude and frequency measurements.

The purpose of monitoring vibration is to detect a mechanical malfunction at the outset of its development. Early detection can help you to either save an expensive machine from failure, or greatly reduce the costs of repairs and down time. On many machines, dangerous conditions of operation can be corrected if the machine is stopped before any damage is incurred. The savings resulting from the use of just one Vibraswitch or Monitor can amount to more money than it would cost to equip an entire plant, refinery or pipeline.

Thousands of large, electrically driven centrifugal fans or blowers are typically protected with only circuit breakers on the driving motors, which will only respond to an over-current condition of the motor. In some cases, temperature monitors are used on anti-friction bearings. Temperature monitors do not respond to unbalance conditions caused by damaged rotors or accumulated deposits, and they often respond too late to a failing bearing. The controls normally installed on large prime movers typically respond to all important variables with, in many cases, one exception -- acceleration or velocity due to vibration. Large machines can, and do, incur failure without any of the conventional protective devices responding. When this happens, it is obvious that something is missing in the protective controls.

If the need for vibration protection is so obvious, why isn’t it standard practice for all large machines to have protective devices specified? Here are some reasons:

1. Vibration is a difficult element to measure, comprehend or compare because it is composed of a variety of fundamental frequencies, higher harmonics and aperiodic components (transients), all of which vary greatly across different machines as well as across different locations on the same machine. The typical prospective user assumes that the only significant quantity to measure is mils (displacement), and even then may have no idea as to what level of mils would be safe.

2. Many potential users rely on the ability of their machinery operators to detect any changes in the sounds their machinery is making, which might indicate mechanical trouble. This dependence on sound is better than nothing, but has important disadvantages: (1) sound, at the fundamental (low) frequency of rotation, is usually inaudible; (2) the human ear is very poor in remembering and comparing sound levels; (3) the sound of a machine is frequently masked by extraneous noise. Another great disadvantage is that constant operator attendance is required. With the trend to automation and unattended or remote operation of machinery, constant operator attendance is not economical, nor is it, in many cases, possible.

This depends on the type of protection you desire. A Vibraswitch will protect you from catastrophic failure by shutting a machine down before excessive damage is incurred, and before it can do harm to nearby personnel (i.e., a fan blade dislodges and causes injury, or possibly death, to an employee).

A Vibraswitch will not, however, give you advanced notice of an impending or a generating problem. To provide you with advanced notice, a Monitor or Stud Mount Accelerometer/Transmitter is needed. These instruments both deliver a 4-20 mADC output. Charting this information output can reveal gradual increases in vibration which indicate that maintenance will be required sometime in the near future. Armed with this information, you can schedule preventative maintenance before a catastrophic failure occurs -- failure which might otherwise prove much more costly and/or occur during a peak production period for that machine, when you can hardly afford downtime.

By recording and trending the 4-20 mADC output, you will be able to track the history of a machine’s performance, which can prove useful for various reasons: (1) it can help you to determine whether or not a preventative maintenance overhaul has been performed properly; (2) it can help you determine at what vibration level you should start your maintenance procedure; (3) it can alert you to unusual vibration increases which may be indicative of pending catastrophic failure.

Additionally, you can purchase a Robertshaw Monitor that has shut down or alarm contacts. With this additional feature, you can have the best of both worlds – trending for preventative maintenance, and immediate shut down or alarm in case of a catastrophic failure. You can also use a Robertshaw Stud Mount Accelerometer/Transmitter alone. Its 4-20 mADC output can be transferred via your PLC, DCS or currently relay for shut down or alarm.

THE BOTTOM LINE: A very small investment can save you thousands or even millions of dollars in excessive repair costs and/or unplanned machinery downtime. It will also make the operating environment safer for your employees.

Robertshaw Vibraswitches Provide:
a. Shutdown/Early Warning before catastrophic failure.
b. Protection for unattended machinery.
c. Predictive maintenance, so that you can schedule maintenance for non-peak production periods.
d. Reduced frequency and severity of machinery losses.
e. Reduced downtime and repair costs, resulting in significant savings.

Robertshaw Monitors/Transmitters Provide:
a. A continuous record of machine vibration over an extended period of time, enabling you to track trends in the information. Vibration "trends" can help you to determine if you need to open and inspect machinery or schedule maintenance/overhaul.
b. A record of short-term variations in machinery under various operating conditions (start-up, load changes, detonation, etc).
c. Detection of machinery degradation early enough to prevent catastrophic failure.
d. Immediate and comparative data to insure a repair or overhaul has been performed properly.
e. Predictive maintenance, so that you can schedule maintenance for non-peak production periods.
f. Reduced frequency and severity of machinery losses.
g. Reduced downtime and repair costs, resulting in significant savings.

a. Start Delay: Start Delay is used in situations where a machine exhibits excessive vibration during its start-up. If the vibration at start-up exceeds the alarm or shut down point of the Vibraswitch or Monitor (equipped with shut down/alarm feature), the Vibraswitch or Monitor will always trip the alarm or shut down the machine during start-up. But with the Start Delay feature, the Vibraswitch or Monitor shut down or alarm mechanism will be disabled during the start-up period. This delay period is either fixed or adjustable, depending on the particular model.

An alternative method of providing a Start Delay is to use the Reset Coil on a Vibraswitch. Energizing the reset coil (with the reset coil voltage rated for that particular model – this could be 24 VDC, 48 VDC, 120 VAC, etc.) will keep the switch from tripping the alarm or shutting down the machine for as long as reset coil remains energized (maximum time allowed is 3 minutes). The voltage must be removed from the coil once the machine has started, thus re-activating the alarm or shut down feature of the Vibraswitch for protection as the machinery continues to run.

b. Monitor Delay: Monitor delay is used in situations where short transient vibrations (detonation, shocks originating external to the machine, load change, etc.) occur while a machine is in operation. If these short transient vibrations exceed the alarm or shut down point of the Vibraswitch or Monitor (equipped with shut down/alarm feature), the Vibraswitch or Monitor will shut down the machine (or trip the alarm) during such transients. With the Monitor Delay feature, the Vibraswitch or Monitor shut down or alarm will be disabled for the duration of the delay period (i.e., 3 seconds). If the excessive vibration is still present at the end of the monitor delay, the unit will then shut down the machine. This feature prevents nuisance shut downs and trips of the alarm due to short duration transients.

c. Start & Monitor Delay: This feature is a combination of both types of Delays outlined above.

These delays may or may not be needed with your particular machine. In many cases, at least some form of Start Delay is required. A word of CAUTION: The solution to a problem with shut down during start-up is NOT to set your set point higher than it should be for ample protection. This will get you through start-up but will NOT provide proper protection for your machine as it continues running. The same applies for Monitor Delay.

This is a common question that should really be answered by the manufacturer of the machine under consideration. Contact the manufacturer's Design Engineering Department and ask two questions:

a. Where are the best places on the machine to mount vibration sensors to achieve the best protection for the machine?

b. At each particular mounting location, what is the normal vibration of the machine in G’s (if purchasing an acceleration device) or inches/second (if purchasing a velocity device), and at what level above that normal vibration would protection for that machine be considered ample?

If the above information cannot be obtained, the Robertshaw Manual you receive with your vibration sensor contains recommended settings based on the "normal" vibration of your machine. However, a word of CAUTION: The settings recommended (and how to arrive at those settings) are based on the premise that the machine under consideration is in proper working condition and is vibrating at its normal level. If your machine is not in proper condition and/or is not vibrating at its normal level, then this method should not be applied.

You should mount the Vibraswitch, Monitor or Transmitter as close as possible to the bearing assemblies, crank shafts, drive gears, or other rotating or reciprocating parts that you want to monitor. This will help to ensure peak responsiveness to malfunctions of these parts.

Any of the vibration instruments can be mounted vertical or horizontal. Please follow the special instructions provided for mounting a Vibraswitch. With a Vibraswitch, the vibration sensing is taken perpendicular to the base of the instrument. Thus, if you want to sense up-and-down movement, you must mount the Vibraswitch on top of a machine; if you want to sense side-to-side movement, you must mount the Vibraswitch on the side of a machine. You will lose 1G of measurement range when mounting on the side as the 1G due to earth gravity is no longer a factor. The switch range will then be, for example, 0G to 3.5G rather than 0G to 4.5G.

The best way to determine placement for mounting is to ask the manufacturer of the machine under consideration. Contact the manufacturer's Design Engineering Department and ask two questions:

a. Where are the best places on the machine to mount vibration sensors to achieve the best protection for the machine?

b. At each particular mounting location, what is the normal vibration of the machine in G’s (if purchasing an acceleration device) or inches/second (if purchasing a velocity device), and at what level above that normal vibration would protection for that machine be considered ample?

If the above information cannot be obtained, the Robertshaw Manual you receive with your vibration sensor contains recommended settings based on the "normal" vibration of your machine. However, a word of CAUTION: The settings recommended (and how to arrive at those settings) are based on the premise that the machine under consideration is in proper working condition and is vibrating at its normal level. If your machine is not in proper condition and/or is not vibrating at its normal level, then this method should not be applied.

Vibration measurements can be taken on nearly all rotating or reciprocating machines. These include fans, blowers, centrifuges, turbines, engines, mills, grinders, alternators, compressors, motors, pumps, generators, gear boxes, etc.

The most common causes include problems with: bearings, connecting rods, pump impellers, drive shaft couplings, lubricating systems, valves and valve lifters, pistons and rings, turbine blades, fan blades, belts and chains, gear teeth, seals, motor windings, cavitating pumps, fans (dirt-laden), belts (fractured), motor armatures, and parts shifting.

Acceleration to velocity conversion is possible on a Vibraswitch, but acceleration to displacement conversion is NOT.

There are formulas you can use to convert from acceleration to velocity or velocity to acceleration, but you must keep in mind that your machine has a basic frequency and other harmonic frequencies associated with its various parts. To accurately calculate the conversion, you will need to convert each of these amplitudes and frequencies, and then add them all together. While the basic frequency of your machine is easily determined (that is, the RPM of your machine divided by 60, which yields Hertz), it is very difficult to measure all of the other harmonic frequencies of your machine unless you measure them with an instrument that will separate and measure each out individually. So conversion is possible, but only after all the frequencies of the machine have been determined. The best solution is to adjust your set point in the same type of measurement used by the instrument you purchased. Or, use a portable vibration meter to measure the vibration of your machine under normal operating conditions, and set it slightly above that for ample protection.

In terms of converting acceleration (G’s) to or from displacement (mils), this can NOT be done. Displacement measures amplitude only. Acceleration and Velocity measurements incorporate both amplitude and frequency, both of which are necessary to measure the true destructive parameters of vibration on reciprocating and rotating machines.