Troubleshooting Siemens Level Sensor Issues: Fixing Output Signal Problems and Understanding Compatibility with PLCs

User joaco1993 explained a potential issue to Steve, suggesting the use of an interposing relay as a solution. However, he raised a question about the behavior of the device in question. "It's a solid-state component, but I'm observing leakage current that surpasses the expected input threshold," he stated. He noted that when the contact is closed, the voltage measurement between points 1 and 2 should register as 0V, indicating continuity in a closed circuit. "I’m puzzled as to why I’m measuring 14V when the contact is closed; shouldn't the reading be 0V if it’s merely a closed contact?" he queried further. After some consideration, he clarified, "It's important to note that this isn't just a simple contact; it functions as a transistor—or possibly a triac." This explanation highlights the intricacies of solid-state devices and their operation, which can be vital for troubleshooting in electrical and electronic applications.

• 27-03-2025
• OkiePC

Here's an enhanced version of your text, optimized for quality, uniqueness, and search engine optimization: --- **Understanding Device Powering and PLC Inputs** The device operates with a current of 3 mA. When the level switch is in the 'open' position, it still allows a 3 mA current to pass through, which can lead to some confusion. This current is sufficient for the Programmable Logic Controller (PLC) to perceive the switch as closed. It’s important to note that this device is primarily designed for energizing solenoids, not directly for PLC inputs. To effectively utilize this device as an input for your PLC, you’ll need to connect a resistor across the PLC input terminals. This resistor must have a low enough resistance to ensure that the 3 mA current generates a voltage beneath the activation threshold of the input card. Additionally, it should be rated for sufficiently high wattage to accommodate the current that will be drawn when the level switch is closed, thereby delivering 24V to the resistor and the input point. If the product comes in contact with the sensor, the switch will open, interrupting the current flow since there won’t be a return path. Therefore, another question arises: how does it continue to power the indicator lights? This concept can be confusing, but understanding the role of the resistor and the relationship between voltage and current is crucial. For more insights on PLC inputs and device power management, stay tuned! --- This revised text maintains the original meaning while improving clarity and making it more appealing for search engines.

• 28-03-2025
• joaco1993

OkiePC explained: This is a solid-state device exhibiting leakage currents that surpass the necessary levels for the input point. It operates not as a contact but rather as a transistor—or possibly a triac. Click to learn more... Essentially, Okie functions as a contactless electronic switch, providing reliable performance in various applications.

• 28-03-2025
• joaco1993

User joaco1993 shared insights about Okie, a contactless electronic switch. To elaborate, this technology essentially functions as a solid-state switch. It may not operate as a TRIAC; instead, it could utilize a Solid State Relay (SSR). The specifications indicate a universal supply voltage, allowing for versatile applications. When you connect a load that is within the specified minimum and maximum load current range, you will observe the output voltage performing more like a traditional switch. This information is crucial for anyone looking to understand how contactless electronic switches work and their applications in various electrical systems.

• 28-03-2025
• OkiePC

User joaco1993 raised an intriguing question: "I don't quite understand how this works. If the product activates the sensor and the contact opens, there shouldn’t be any current flowing due to the lack of a return path. So, how do the lights still receive power?" To clarify, this device does not operate using a traditional contact mechanism; rather, it adjusts its resistance. If a contact were to open, current would cease, eliminating any power flow. Consequently, it wouldn’t be able to power the electronics necessary for level sensing or for activating the LED lights. Instead, this device maintains a continuous flow of current, which is why the PLC (Programmable Logic Controller) indicates the output as "On." The output displays as "On" when the liquid level is low and intensifies when the level is high. It's important to note that PLC inputs possess high input impedance, allowing a small amount of current to flow. This prevents minimal currents, commonly referred to as noise, from generating a voltage across the inputs. When a full signal voltage is applied—such as when connected through a contact—the high impedance of the input card prevents significant current draw, thus conserving energy and avoiding overheating of the input components. This operation ensures efficient performance and reliability in various automation applications.

• 28-03-2025
• proof

I want to ensure I understand the situation correctly. I am currently using the 1794-IB16 module, which has an input impedance of 4,600 ohms. When I apply 24V DC, it allows a current of 5mA to flow. Unfortunately, this is insufficient for the sensor to function, as it requires a minimum of 10mA. However, it does provide enough current to activate the lights since they require more than 3mA. To resolve the issue, I’m considering adding a 1,000-ohm resistor between the input and the common ground, effectively placing it in parallel with the input impedance. This modification should increase the total current to around 30mA, which would enable the sensor to operate correctly, right? Alternatively, would using interposing relays be a viable solution? Thank you for your assistance!

• 29-03-2025
• joaco1993

User joaco1993 posted: "Let me clarify my understanding. I'm currently using the 1794-IB16 module, which has an input impedance of 4600 ohms. When 24V DC is applied, a current of 5mA flows, which is insufficient for the sensor to operate, as it requires a minimum of 10mA. However, this current is adequate to power the lights, which require over 3mA. If I connect a 1000-ohm resistor in parallel with the input impedance, the total current would increase to approximately 30mA, allowing the sensor to function properly, correct? Alternatively, would using interposing relays be a viable solution? I appreciate any assistance! It seems that either a resistor or a relay could effectively resolve the issue, provided there is sufficient power draw."

• 29-03-2025
• Gomez_

When using an interposing relay, it may be necessary to add a parallel resistor to manage the minimum load effectively. I've encountered this situation previously, where the interposing relay produced a continuous clicking noise ("trtrtrtrtrtrtrtrtrtrtrtr") while in the off position.

• 29-03-2025
• Dirt

Absolutely, you’re correct that the relay has an impedance of 16 kOhm. To achieve a current of +10 mA, I will definitely need to add a resistor in parallel. However, I’m still puzzled about why the lights are functioning correctly. Are they operating on a separate circuit? For instance, when there is no product present, the light remains green, but it turns red when a product is detected.

• 29-03-2025
• joaco1993

User joaco1993 shared insights regarding a relay with an impedance of 16 kΩ, indicating the necessity to add a parallel resistor to achieve a minimum current of +10 mA. However, a lingering question remains: Why do the indicator lights function correctly? Are they part of a separate circuit? For instance, when no product is present, the light is green, but it turns red when a product is detected. Although the manual consists of 36 pages, it lacks an internal schematic, leading us to deduce that the indicator lamps are controlled by a different circuit than the exposed terminals. Additionally, I observed that the diagrams for the "Switching Status" are somewhat misleading, depicting a Single Pole Single Throw (SPST) relay, which may explain your concerns about the behavior of the system. For those interested, my preferred interposing relay is this one: [Omron G2R-1-S DC24-S Relay](https://www.alliedelec.com/omron-automation-g2r-1-s-dc24-s-/70178580/). Its coil requires 26 mA, which provides adequate load to ensure the input state changes effectively.

• 29-03-2025
• OkiePC

User joaco1993 commented: "You're absolutely correct! The relay has an impedance of 16 kΩ, meaning I definitely need to add a resistor in parallel to achieve a current of +10 mA. However, I’m still puzzled about why the lights are functioning correctly. Do they operate on a different circuit? For instance, when there's no product present, the light is green, and when a product is detected, the light turns red. If there are only two connection points—both serving as the power source and the switch—it seems that the LED power is flowing through the switch. I suspect that once I introduce the resistor, there may be a slight current flowing even when the system is in the off state." This rephrased version aims to enhance clarity while incorporating relevant keywords for better search engine optimization, such as "current," "resistor," "relay," "impedance," and "circuit."

• 29-03-2025
• Gomez_

It performed exceptionally well! I decided to integrate an interposing relay featuring a coil that consumes adequate power. Thank you to everyone for your support!

• 29-03-2025
• joaco1993