Sensors Frequently Asked Questions
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Question:
Can proximity sensors be connected in series?
Answer
Yes.
The number of proximity sensors connected in series is dependent on the available voltage to energize the PLC input or load. This voltage is calculated as the sum of voltage drops across each sensor subtracted from the available power supply voltage.
Let's use as an example three of the AutomationDirect APS24 series 3-wire NPN sensors,
- Brown wire is positive (+DC)
Blue wire is the negative (-DC)
Black wire is the output
The load will be a PLC input. By connecting the sensors in series, all of the sensors must be activated in order for the PLC to receive an input signal.
- Start by connecting the brown wire of each sensor to the positive terminal (+) of a 24 VDC power supply.
Connect the first sensors blue wire to negative terminal (-) on the 24VDC power supply
Connect the first sensor's black wire to the second sensor's blue wire
Connect the second sensor's black wire to the third sensor's blue wire
For the final termination, connect the third sensor's black wire to the PLC input terminal.
You will need +24VDC on the input modules common terminal, for the input to work correctly.
You can continue this patterns as many times as needed, staying within the voltage restrictions previously mentioned.
FAQ ID: 303
Question:
What is the smallest AC powered proximity sensor that AutomationDirect offers?
Answer
The smallest AC powered sensor is 8mm V3E1 Series Sensors
FAQ ID: 305
Question:
Does AutomationDirect offer capacitive type proximity sensors?
Answer
Yes, there are many different types of capacitance sensors. Please see Capacitive Proximity Sensors for the different selections.
FAQ ID: 306
Question:
What is the operating voltage for AutomationDirect proximity sensors?
Answer
The majority of AutomationDirect proximity sensors operate at 10-30 volt DC power. However, there are sensors that operate in the 10 - 250 VAC range and 20 - 250 VDC range.
Please see the web site's Sensors and Encoders section for all the different models.
FAQ ID: 307
Question:
Can I connect only two wires of a 4-wire sensor?
Answer
A 4-wire sensor is designed for use of at least three of the four wires. Two of the wires are used to power the sensor (+ and - voltage). The other two wires are used for outputs, either a Normally Open (N.O.), Normally Closed (N.C.) output, or both outputs. The sensor will not operate as a 2-wire device.
FAQ ID: 309
Question:
What is the minimum distance that two proximity sensors can be installed parallel to each other?
Answer
When placing sensors parallel to each other, always leave a minimum distance equal to the diameter (12mm, 18mm or 30mm)of the sensors.
FAQ ID: 310
Question:
Does AutomationDirect offer sensors that are protected against washdown?
Answer
Yes, the majority of sensors offered by AutomationDirect have an IP67 rating, which is rated for brief, intermittent submersion. Always check the specifications before selecting a device for any application.
FAQ ID: 339
Question:
What is the difference between inductive and capacitive sensors?
Answer
The primary difference is sensing material. Inductive sensors only detect metallic objects while capacitive sensors will detect other materials such as wood, paper, liquids, cardboard, etc.
FAQ ID: 340
Question:
Why is switching frequency important?
Answer
Switching frequency is the speed in which a sensor detects an object, resets, and senses another object. For example, if a sensor has a switching frequency of 100 Hz (100 cycles peer second) it can detect a maximum of 100 objects per second. This is very critical in many applications such as gear rotation measurement.
FAQ ID: 341
Question:
Does AutomationDirect offer an AC proximity sensor in a quick-disconnect model?
Answer
Yes, the V Series AC/DC Sensors are available with quick disconnects. They come in 8, 12, 18, and 30mm sizes.
They can be used with the Connection Cables also offered by AutomationDirect.
FAQ ID: 404
Question:
Does AutomationDirect offer TTL sensors?
Answer
Sorry, AutomationDirect does not offer TTL sensors at this time.
FAQ ID: 405
Question:
How do I know what size proximity sensor to use?
Answer
It depends on two factors: (1) mounting space and (2) sensing distance. Each application has a specific amount of space available for the sensor and a requirement of how close the sensor can be mounted to the sensing object.
FAQ ID: 457
Question:
What is the difference between a shielded and unshielded proximity sensor?
Answer
There are two major differences between a shielded (flush) and an unshielded (non-flush) proximity sensor.
- With a shielded sensor, only the face of the sensor is exposed and can be mounted flush on the mounting surface. In some applications flush mounting is a requirement.
With an unshielded sensor, the face and a small portion of the sides are exposed. This allows detection of objects from the side as well as the front, but does not allow mounting flush on the mounting surface, as the sensor would always be activated.
FAQ ID: 458
Question:
How do I determine which type of proximity sensor output I need, NPN or PNP?
Answer
PNP sensors are current sourcing devices and NPN sensors are current sinking devices.
A current sourcing sensor must be connected to a current sinking input. Likewise, a current sinking sensor must be connected to a current sourcing input, so you must know the input circuitry of the device you are connecting with the sensor.
Most AutomationDirect PLC input modules (except 305 series) allow NPN or PNP sensors to be connected. This is sometimes determined by what other type of devices are being connected to the PLC module.
FAQ ID: 459
Question:
How do I choose between a Normally Open (NO) and Normally Closed (NC) sensor ouput?
Answer
Normally Open sensors do not pass power to the PLC until an object is detected. Normally Closed sensors always pass power to the PLC until an object is detected. The majority of AutomationDirect sensors have Normally Open outputs, however, there are many sensors available with Normally Closed outputs as well.
FAQ ID: 460
Question:
Why use a sensor with a quick-disconnect cable versus an axial cable?
Answer
A sensor with a quick-disconnect cable allows for easy replacement of the sensor by eliminating the need for rewiring. This is important when considering machine or operation downtime associated with replacing a sensor. There is a cost difference versus a sensor with an axial cable since the quick-disconnect cable must be purchased seperately.
FAQ ID: 461
Question:
What is the difference between 2-wire, 3-wire, and 4-wire sensors?
Answer
2-Wire Sensors: Allows either NPN or PNP output (Typically AC powered sensors)
3-Wire Sensors: Most commonly used. When ordering, must choose an NPN or PNP output
4-Wire Sensors: Allows either NO or NC output (Don't have to select!) Must choose NPN or PNP output when ordering
FAQ ID: 462
Question:
Can a proximity sensor be installed in a vibrating environment?
Answer
Yes, please check the sensor's data sheet for vibration specifications.
FAQ ID: 482
Question:
What is the leakage current of an AutomationDirect proximity sensor?
Answer
AutomationDirect offers a wide range of proximity sensors, with each model having its own specifications. To find the leakage current for a particular sensor, reference the Technical Specifications table for the sensor. The table can be located on the specific sensor's product page by clicking the "Technical Specifications" link.
FAQ ID: 547
Question:
Can you parallel ac inductive sensors?
Answer
Yes.
FAQ ID: 617
Question:
Does AutomationDirect offer an AC sensor with a Normally Closed output?
Answer
Yes, the V Series AC/DC Sensors have a normally closed contact. They are available in 8, 12, 18, and 30mm sizes,
FAQ ID: 618
Question:
Will a magnet trip an inductive proximity sensor?
Answer
If there is a sufficient amount of ferrous metal in the magnet there is the possibilty of the sensor becoming activated.
FAQ ID: 679
Question:
Does AutomationDirect offer a photoelectric sensor that is submersible??
Answer
The majority of photoelectric sensors offered by AutomationDirect have an IP67 rating, which is protected against the effects of temporary immersion between 15cm and 1m, with a tested duration of 30 minutes. These sensors are not recommended for continuous immersion applications.
FAQ ID: 766
Question:
Does AutomationDirect offer an AC powered photoelectric sensor?
Answer
Yes, AutomationDirect offers three series of AC photoelectric sensors. The MQ series and the MV series.
FAQ ID: 933
Question:
What type of rubber is used for the rubber boot on the ABM series of limit switches offered by AutomationDirect?
Answer
NBR 55 (Nitrile Butadiene Rubber 55 Shore)
General Description:
Also known as Nitrile Butadiene (NBR), or Buna-N. It is a copolymer of butadiene and acrylonitrile which makes it exceptionally resistant to petroleum based oils and hydrocarbon fuels. It is also good against fats, greases, and some chemicals. Nitrile Rubber has a temperature range of -40F to +250F.
FAQ ID: 949
Question:
How do inductive proximity sensors work?
Answer
Inductive proximity sensors are used to detect the presence of metallic objects without actually contacting the object. Their high-speed switching and small size make them indispensable in automation applications.
Inductive proximity sensors consist of an oscillator driven coil. The oscillator creates an electromagnetic field which appears at the active face of the sensor. If a metal target enters this area, the electromagnetic field is reduced and the sensor switch turns on or off.
Some typical inductive sensor applications are: counting metallic objects, monitoring the position of elements in a machine, sensing the presence of metallic parts such as screws, and measuring the rotational speed of axial detecting cams.
FAQ ID: 1053
Question:
What is the difference between the PUR (polyurethane) and PVC (polyvinyl chloride) sensor cables.
Answer
Use PUR (polyurethane) jacket for oily and direct sunlight applications. Use PVC (polyvinyl chloride) jacket for typical industrial applications
FAQ ID: 1118
Question:
How do I adjust the SET and RESET on the PSD25 series sensors?
Answer
The SET and RESET adjustments (Rings) are mechanically interlocked to prevent setting less than the minimum offset required by the sensor. You cannot use the same pressure setting for the SET and RESET. There must be some hysteresis (offset) to the settings.
All the directions assume you are looking at the cable end of the sensor.
- Unlock the sensor adjustments (top most ring). The unlock symbol will line up with center arrow when unlocked.
- Rotate the LOCK ring clockwise until it stops.
- Adjust the SET point (2nd ring from top) to it's lowest setting.
- Rotate the SET ring counter-clockwise until it stops.
- The RESET ring will start moving at some point to maintain the mimimum offset.
- Adjust the RESET point (3rd ring from top) to the desired reset point. This is the pressure at which the sensor will turn off after being turned on. This has to be offset from the SET to prevent chattering/rapid cycling.
- Rotate the RESET ring clockwise to the desired reset point. - The SET will move also to maintain the offset.
- Check the setting of the SET ring. You cannot adjust the SET point lower than the reset so the reset may move.
- If this needs to be adjusted, the RESET will be affected to maintain the offset.
FAQ ID: 1181
Question:
What does the 'TV' specification mean?
Answer
Time Delay Before Availability refers to the time between when power is first applied to the sensor and when it is ready for operation. In this period lasting only a few milliseconds, the output may be at an unpredictable state. This is not to be confused with 'Switching Frequency', which is how fast the sensor can change output states.
FAQ ID: 1277
Question:
Can a proximity sensor be used to determine RPM?
Answer
Yes, subject to a number of factors. It must be connected to a high-speed counter capable of reading the pulse rate. The sensors switching frequency must be higher than the rate at which the rotating target is passing the sensor. The target must be present long enough for the sensor to switch a valid signal to the counter. The 'off' portion of the target should be about twice the 'on' time.
FAQ ID: 1278
Question:
How accurately can a proximity sensor control positioning?
Answer
A proximity sensor will typically be able to repeatedly sense a target within 5% (+/-) of the same distance. When a short range (usually smaller) sensor is used, this can result in very good accuracy. Conversely, if only the presence of a target needs to be known, use a longer-range, or more sensitive sensor.
If you need very precise target location, you might want to look at the Precision Limit Switches
FAQ ID: 1279
Question:
What kind of connectors do the sensors use?
Answer
The sensor connector varies, depending on which sensor you are using. Typically it will be a M8, M12, or 1/2" connection. Check the product specifications for the appropriate cable connection.
FAQ ID: 1280
Question:
What is the difference between 'Light-on' and 'Dark-on'?
Answer
This refers to if the photosensor is detecting its own light source when its normal output is 'on'. A diffuse sensor is normally 'light-on', since its output is on when its own light source is reflected from a target. Retroreflective and thru-beam sensors are normally 'dark-on', since the output is active when the light beam is blocked. Note that several sensors may be configured to either a 'light-on' or 'dark-on' mode of operation.
FAQ ID: 1281
Question:
How is the range of a 'Diffuse' sensor determined?
Answer
'Diffuse' sensor range is dependant on the reflectivity of the target. In some cases, a dark object may reflect light better than a light-colored object. For purposes of comparison, diffuse sensors are specified by the distance at which they detect white card stock.
FAQ ID: 1282
Question:
Do you have material influence tables for the capacitive proximity sensors such as the CT series ?
Answer
The official answer is that there really is not an official reduction chart available mostly because of the different effects of the materials, thickness, humidity, the trimmer position and such. Even more, the international standard (IEC60947-5-2) which the sensors are tested to and such does not give the rules to calculate such reductions.
There are several factors that can influence range such as target conductivity, humidity and temperature.
- Here are some very general correction factors
- Steel 1.00
- Surface of water 1.0
- Ungrounded Steel(150x150x1mm) .85
- Glass (150x150x7.5mm) .55
- PVC (150X150X4mm) .15
FAQ ID: 1379
Question:
On the SU1, SU2, and TU1 ultrasonic sensors, how does the CONTROL wire work?
Answer
Control Wire NOT connected : sensor functions normally (ie, turns on/off relative to presence of target)
Control Wire connected to ground : sensor output maintains last output (on/off) until removed from ground. (Basically freezing sensor in the last state)
When multiple sensors are in close proximity it is recommended to connect the control wires together. This forces the sensors to emit at the exact same time. This reduces the interference risk because when the beam of one sensor reaches the other one, its energy is faded to a point it is not detected.
FAQ ID: 1382
Question:
How do I adjust for NO vs. NC operation of the BX80B-1P-0H light screen sensor receiver?
Answer
First, in order to change the shelf state of the receiver from normally open to normally closed, the commutator adjustment must be made with the receiver powered down.
Changing the commutator setting with power applied to the receiver has no affect as the receiver only reads this setting on power up. This is briefly documented in the product insert.
Second, changing the setting with the receiver powered up does NOT damage the receiver.
Third, normally open and normally closed operation of the sensor is with the sensor blocked. The operation is contrary to the traditional understanding of normally open, normally closed and shelf state. This is built into the Micro Detectors design of the sensor, and thus cannot be changed.
Rotating the commutator fully counter-clockwise sets the receiver to NO operation (output OFF with target blocking beam) and rotating the commutator fully clockwise sets the receiver to NC operation (output ON with target blocking beam).
FAQ ID: 1444