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【Notification of Manufacturer Change for Panasonic Industrial Devices SUNX Products and Panasonic Industrial Devices SUNX Tatsuno Products】
From April 1, 2024, the terms "Panasonic Industrial Devices SUNX Co., Ltd." and "Panasonic Industrial Devices SUNX Tatsuno Co., Ltd."
in this page and in the manuals and other documents to be downloaded will all be replaced with "Panasonic Industry Co., Ltd." and applied accordingly.
Business > Industrial Devices > Automation Controls Top > FA Sensors & Components > Timers / Counters / FA Componets > Timers > LT4H-W Digital Timers(DIN 48)(Discontinued Products) > Cautions For Use
We are sorry, the products have been discontinued. Please refer to the details of the discontinued products and the recommended substitutes list below.
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In the circuit that switches an inductive load, a contact failure may occur at a contact point due to surge or inrush current resulting from that switching.
Therefore, it is recommended that the following protective circuit be used to protect the contact point.
Circuit | Application | Features/Others | Device Selection | |||
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AC | DC | |||||
CR circuit (r: resistor c: capacitor) |
* Note: | Available | If the load is a relay or solenoid, the release time lengthens.Effective when connected to both contacts if the power supply voltage is 24 or 48 V and the voltage across the load is 100 to 200 V. | If the load is a timer, leakage current flows through the CR circuit causing faulty operation. Note: If used with AC voltage, be sure the impedance of the load is sufficiently smaller than that of the CR circuit. |
As a guide in selecting r and c, c: 0.5 to 1 µF per 1 A contact current r: 0.5 to 1 ohm; per 1 V contact voltage Values vary depending on the properties of the load and variations in timer characteristics. Capacitor c acts to suppress the discharge the moment the contacts open. Resistor r acts to limit the current when the power is turned on the next time. Test to confirm. Use a capacitor with a breakdown voltage of 200 to 300 V. Use AC type capacitors (non-polarized) for AC circuits. |
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Available | Available | |||||
Diode circuit | N/A | Available |
The diode connected in parallel causes the energy stored in the coil to flow to the coil in the form of current and dissipates it as joule heat at the resistance component of the inductive load. This circuit further delays the release time compared to the CR circuit.(2 to 5 times the release time listed in the catalog) |
Use a diode with a reverse breakdown voltage at least 10 times the circuit voltage and a forward current at least as large as the load current. In electronic circuits where the circuit voltages reverse breakdown voltage of about 2 to 3 times the power supply voltage. |
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Varistor circuit | Available | Available | Using the rated voltage characteristics of the varistor, this circuit prevents excessively high voltages from being applied across the contacts. This circuit also slightly delays the release time. Effective when connected to both contacts if the power supply voltage is 24 or 48 V and the voltage across the load is 100 to 200 V. |
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The type of load and its inrush current characteristics, together with the switching frequency are important factors which cause contact welding. Particularly for loads with inrush currents, measure the steady state current and inrush current and use a relay or magnet switch which provides an ample margin of safety. The table below shows the relationship between typical loads and their inrush currents.
Type of load | Inrush current |
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Resistive load | Steady state current |
Solenoid load | 10 to 20 times the steady state current |
Motor load | 5 to 10 times the steady state current |
Incandescent lamp load | 10 to 15 times the steady state current |
Mercury lamp load | 1 to 3 times the steady state current |
Sodium vapor lamp load | 1 to 3 times the steady state current |
Capacitive load | 20 to 40 times the steady state current |
Transformer load | 5 to 15 times the steady state current |
When you want large load and long life of the timer, do not control the load direct with a timer. When the timer is designed to use a relay or a magnet switch, you can acquire the longer life of the timer.
Since PM4H and LT4H series timers use a transformerless power supply system, the input equipments must have the power supply transformer in which the secondary side is not grounded with the primary and secondary sides insulated, in order to prevent interference of the power supply circuit when connecting the external input circuit as Fig. A.
Be sure not to use an autotransformer. In case of secondary side grounded or using the autotransformer, this product may be destroyed due to short circuit electrically as Fig. B (1 and 2).
In case of F.G. terminal of equipments such a PLC grounded in secondary side of the transformer, inner circuits of this product and the input equipment may be destroyed due to short circuit electrically as Fig.B (3).
Therefore, use the isolated type timers or do not ground F.G. terminal of the products.
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Long continuous current flow through the timer (approx. one month or longer) cause generation of heat internally, which degrade the electronic parts. Use the timer in combination with a relay and avoid long continuous current flow through the timer.
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If the operation voltage for the timer is turned ON after the limit time operation is completed or before the limit time is reached, the Power off time longer than the timer restoration time must be secured.
If the timer is restored immediately after the specified time is reached, the circuit must be configured so that the restoration time of the timer can be secured sufficiently.
If the power circuit for the timer is turned OFF with the timer contact, a suicide circuit may be configured (Fig. A). In order to settle the problem with this potential suicide circuit, the circuit must be designed so that the timer is turned OFF after the self-retention circuit is completely released (Fig. B).
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The electrical life varies depending on the load type, the switching phase, and the ambient atmosphere. In particular, the following cases require careful attention:
The effective countermeasures include:
Correctly connect the pins while seeing the pin layout/connection diagram. In particular, the DC type, which has polarities, does not operate with the polarities connected reverse. Any incorrect connection can cause abnormal heating or ignition.
Rectification type | Ripple percentage |
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Single-phase, full-wave | Approx. 48% |
Three-phase, full-wave | Approx. 4% |
Three-phase, half-wave | Approx. 17% |
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For the superimposed surge of power supply, the standard waveform (±1.2×50μs or ±1×40μs) is taken as the standard value for surge-proof voltage.
(The positive and negative voltages are applied each three or five times between the power pins.)
For the standard values for the PM4H, LT4H, and S1DX type timers, see the respective items in "Caution on usage."
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PMH [±(1×40)μs]
Voltage type | Surge voltage |
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AC type (except 24V AC) | 4,000V |
12V, 24V DC, 24V AC | 500V |
Other timers [±(1×40)μs]
Type | Surge voltage |
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PNS CN-C CHP, CHP-F | 20 times rated voltage |
CHP-SD | 4,000V |
If external surge occurs exceeding the specified value, the internal circuit may break down. In this case, use a surge absorption element. The typical surge absorption elements include a varistor, a capacitor, and a diode. If a surge absorption element is used, use an oscilloscope to see whether or not the foreign surge exceeding the specified value appears.
Do not change the set time when the limit time operation is in progress.
However, this is possible only with the motor-driven type timer if the set time is shorter than the remaining time. For changing the set time on the digital timer (LT4H), see the relevant item in "Caution on use."
In order to increase the reliability in the actual use, check the quality of the timer in the actual usage.
The power circuit has no transformer. When an input signal is applied to two or more timers at once, do not operate the power circuit in an independent way. If the timer is powered on and off independently as shown in Fig.A, the timer's internal devices may get damaged. Be careful never to allow such wiring. (Figs. A, B and C show the circuitly for the 11-pin type.)
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If independent power operation must be used, keep the input contacts or transistors separate respectively, as shown in Fig.B.
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When power operation is not independent, one input signal can be applied to two or more counters at once, as shown in Fig.C.
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* | The short-circuit impedance should be less than 1 kohm. [When the impedance is 0 W, the current coming from the signal input and stop input terminals is approximately 12 mA, and from the reset input and lock input terminals is approximately 1.5 mA.] Also, the open-circuit impedance should be more than 100 kohm. |
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* | As shown in the diagram below, from a non-contact point circuit (proximity switches, photoelectric switches, etc.) with a power supply voltage of between 12 and 40 V, the signal can be input without using an open collector transistor. In the case of the diagram below, when the non-contact point transistor Q switches from off to on (when the signal voltage goes from high to low), the signal is input. |
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* | Not related to the start input. |
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The operation mode and time range can be set with the DIP switches on the side of the timer. Make the DIP switch settings before installing the timer on the The operation mode of LT4H-W series can be set with the keys and switches on the front of the timer.
Operating voltage | Surge voltage(peak value) |
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AC type | 6,000V |
DC type 24V AC type |
1,000V |
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Power supply terminals | Input terminals | ||
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AC type | DC type 24V AC type |
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Noise voltage | 1,500V | 1,000V | 600V |
wave form (noise simulator)
Rise time: 1 ns
Pulse width: 1 μs, 50 ns
Polarity: ±
Cycle: 100 cycles/second
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Please abide by the conditions below when using in applications that comply with EN61812-1.
This timer is protected with basic insulation and can be double-insulated to meet EN/IEC requirements by using basic insulation on the load.
Requests to customers (Automation Control Components & Industrial Device) [Excluding specific product]
Requests to customers (Automation Control Components & Industrial Device) [For specific product]
Requests to customers (FA Sensors & Components [Excluding motors])
Requests to customers (Dedicated to industrial motors)