Let’s talk about connection diagrams.  Although sensor hookup is typically simple – just a few wires – it’s always a good idea to consult the connection diagram before wiring to be sure you’ll end up with the outcome you expect. Most diagrams follow a pattern where the industrial sensor connections are shown on the left, and the load and power supply to be connected are indicated to the right.  If no load is shown (it usually appears as a small unlabeled box), one should be assumed.  This is the component or circuit that will see the switching or analog output of the sensor – common examples are a relay coil or PLC input. The majority of electronic sensors require power for operation.  Two-wire sensors have only two connection points, so the output is wired in series with the power supply.  For other configurations, power is supplied to the sensor using two connection points, and the output is on a third wire.  The supply voltage range varies depending on the sensor specifications, and may be DC, AC, or AC/DC. 

Power supply connection points are pictured on a diagram using a variety of symbols as follows: For AC power supplies: ~, L1 and L2, L and N For DC power supplies: +UB and 0V, +Ub and -Ub, L+ and L- Sensors with switching output The main function of many industrial sensors is to act as an electronic switch.  If a sensor has switching output, this will be pictured on a connection diagram in different ways depending on the type of sensor you’re working with. Inductive, capacitive, or magnetic sensors For these three types of sensors, the switching output is usually shown inside the box that represents the sensor, and appears as an open or closed contact.  This is the normal state of the switch, which is when no activating target is in the sensor’s detection field.  Connection diagrams for 3- or 4-wire sensors will also show the required wiring configuration for their type of output:Current-sourcing (PNP) outputs are internally connected to the power supply voltage, and so should be wired externally to a load that has a connection to DC ground.

Current-sinking (NPN) outputs are internally connected to DC ground, and so should be wired externally to a load that has a connection to the power supply voltage. Ultrasonic or photoelectric sensors These sensors are more likely to have multiple switching outputs, or outputs that are programmable, and a contact is generally not shown.  Instead, outputs are marked by symbols such as Q1 and Q2, or light ON and/or dark ON circles, to show different modes of operation. If a switching output is strictly PNP or NPN, the external connection through the load may be shown as described above.  In the case of a push-pull output, this will not be part of the connection diagram, since sensors with this output can operate using either type of external wiring configuration. Sensors with analog output Some sensors feature analog output, which changes in a linear fashion according to some distance traveled by the target in relation to the sensor’s detection field.  Analog output can be shown on connection diagrams using the symbols or labels shown below.

Sometimes there will be an input connection on the sensor, which is used for Teach-in, mode selection, or another programming function.  These are described in the sensor data sheet and labeled accordingly on the connection diagram; some common labels are IN, XI, Test, Sync, or ET. Class 2 or Class II Class 2 is a classification referring to the NEC – National Electric Code.  To avoid potential cable overheating due to excessive currents and electric shock, the output of the power supply is limited to 60VDC or 100VA, (100W when used with an AC-DC power supply).  hvac unit with heat pumpYou will often see 24V output DIN rail power supplies or LED drivers rated at 91W rather than 100W because if the power supply is overloaded, any tolerance in the over current protection has to be accounted for. how to fix my ac compressor

Often these products will be certified to UL1310 and will list this in the datasheet.  An example of this is TDK-Lambda’s DSP series.  You can see from the model selector list on page 2 of the DSP datasheet that output currents of 4.2A or greater are not approved to UL1310. Class II (with Roman numerals) refers to power supplies with either a double or reinforced insulation barrier between the input and the output. electric furnace and ac unitsClass II supplies do not rely on an earth connection to protect against shock hazard. Many cell phone chargers and laptop power supplies are Class II.  TDK-Lambda’s DSP series also are Class II, having just a Line and Neutral AC input without a ground connection. A Class II power supply rating label will show this symbol: One advantage of Class II is better surge protection between input and ground and usually a lower earth leakage current. What useful feature does a power supply bleeder resistor provide?

It ensures that the filter capacitors are discharged when power is removed It acts as a fuse for excess voltage It removes shock hazards from the induction coils It eliminates ground loop current Which of the following components are used in a power supply filter network? What is the peak-inverse-voltage across the rectifiers in a full-wave bridge power supply? Equal to the normal peak output voltage of the power supply One-quarter the normal output voltage of the power supply Half the normal output voltage of the power supply Double the normal peak output voltage of the power supply What is the peak-inverse-voltage across the rectifier in a half-wave power supply? Two times the normal peak output voltage of the power supply One-half the normal peak output voltage of the power supply One-half the normal output voltage of the power supply Equal to the normal output voltage of the power supply What portion of the AC cycle is converted to DC by a half-wave rectifier?

What portion of the AC cycle is converted to DC by a full-wave rectifier? What is the output waveform of an unfiltered full-wave rectifier connected to a resistive load? A series of DC pulses at twice the frequency of the AC input A series of DC pulses at the same frequency as the AC input A sine wave at half the frequency of the AC input Which of the following is an advantage of a switchmode power supply as compared to a linear power supply? High frequency operation allows the use of smaller components Faster switching time makes higher output voltage possible Fewer circuit components are required All of these choices are correct Which symbol in figure G7-1 represents a field effect transistor? Which symbol in figure G7-1 represents a Zener diode? Which symbol in figure G7-1 represents an NPN junction transistor? Which symbol in Figure G7-1 represents a multiple-winding transformer? Which symbol in Figure G7-1 represents a tapped inductor?