Hello everyone! After conducting extensive research on various forums and blogs, it appears that the 1794-VHSC module is not popular among users. I encountered some issues myself while using this module to count pulses from a flow meter. Initially, I was unsure if I needed the module or if a digital input would suffice. Luckily, the flow meter offers a scalable pulse output feature, which I have set to 100:1. My inquiry consists of two parts. Firstly, does anyone have information on the correct wiring for this module? I managed to get it to count on the A input, although the manual indicates that the A indicator should be flashing. After discussing with a colleague, we connected 0V to the A- terminal, which resolved the issue. However, we noticed that the pulses were rising even when there was no flow, and the count exceeded 1000 pulses after reaching the target. The manual specifies that the A and A_ inputs are 24V, possibly intended for an encoder (with which I have limited experience). Do I need a 0V reference for the card to function properly? Secondly, has anyone encountered faults with this module? It worked flawlessly for several days before suddenly starting to flash (not to be confused with the 1794-AENTR module). Despite checking the power supply, ensuring it was not in PROG mode, and verifying network connections, status bits like Status.1 and Status.15 were set to one. The flashing module prevented pulse capture, with no active filters and a rollover set to 16777215. The PLC in use is the 1769-L30, housed in a rack containing an AENTR, digital input/output modules, analog input module, and the VHSC module. Overall, it seems like a configuration issue is at play, but I'm unsure of the exact cause. Let's continue troubleshooting together!
Are you using a flow meter with a specific type of output and voltage? Most discrete modules have a 0V common reference and require a +24V supply for each input. However, encoders often use differential signaling for noise immunity. The VHSC was designed to accommodate these signals. To use a single-ended device with a differential input, connect the DC Common to the -Signal terminal as suggested by your colleague. For a single pulse generator, connect the flowmeter output to +A and the flowmeter DC common to -A. Refer to Page 19 of the user manual for a diagram illustrating a mechanical dry contact connected to the second counter's Z-input. The -Z is linked to the module DC Common, while the +Z goes through the dry contact to the module +24V power, combining the module's logic power and input channel power. One common issue across the FLEX line is that using the same power supply for the network adapter and analog/specialty I/O modules can sometimes cause the network adapter to not recognize the analog/specialty module during startup. To address this, add a timing relay to ensure specialty modules boot up before the I/O Adapter. If the module is accumulating pulses when there is no flow, check if the input is flashing, indicating a signal that is recognized as a pulse. Using an oscilloscope or scopemeter can help analyze signals of this nature. In Counter mode, the module will continuously count without stopping at the preset value. It will only stop counting if a Reset pulse or software Reset command is received. For flow meter applications, it is recommended to set the module in Rate Measurement mode to count pulses on Channel A over a defined period and provide both a pulse count and pulses/time rate.
I am also confused about the possible configuration error. Can you specify where you observed the setting of Bit 1 and Bit 15?
Dear @Ken Roach, I took some time to research the terminology you mentioned (single vs diff) to gain a better understanding of these circuits. The diagram shows the recommended connection method by the OEM for the pulse output, which is an open-collector type utilizing an optocoupler. The TurbineInc meter is powered by a 24VDC source connected to terminal 5 with a 1.5Kohm pull-up resistor, approved by the OEM. From terminal 5, the power goes to the A input while terminal 6 receives 0V. The OEM suggests using a separate power source for the meter instead of loop power. Initially, I had loop power connected, but I switched to battery operation, as the pulses were erratic when using loop power. Despite following recommendations and making adjustments, the pulses continued to exhibit irregular behavior even when the system was not running, overshooting by about 1000 pulses before stabilizing. I also encountered issues with lost pulses, indicated by an "E" status on the flow meter monitor, with approximately 50-60% of pulses being lost. The screenshots display this status in the monitor tag section of the controller tags. Upon inspecting the vhsc counter module, no faults were detected, but active bits were present in the status section, based on WORD values. It appears that configuration-related issues were causing the erratic behavior, as even after making recommended changes to eliminate errors from the flow meter monitor, the pulses continued to fluctuate. The status.14 bit seemed active, as per the saved data before going offline.
Hello, @AD-PLC! I am experiencing a problem similar to yours. Have you discovered any solutions for your issue yet? Thank you for your help!
Within the 1794-VHSC setup, the counters tab includes various filtering options. I currently have filtering enabled for A, B, and Z. However, if these filters are not set, my pulse count fluctuates.
Hello, it's indeed puzzling that your 1794-VHSC module is reading pulses when there's no flow. However, this could be due to electrical noise or a grounding issue, I recommend you double-check your shielding and grounds. On your first point, you do require a 0V reference for the module although it's important to ensure that it's tied back to the same 0V on the 24V power supply for the module/encoder. For the flashing light issue, you've covered most of the common troubleshooting steps. One thing I'd suggest checking is the network communication, an excessive network load could potentially cause erratic behavior. Also, the 1794-VHSC high-speed counter module does have the notorious reputation for being temperamental, have you thought about bearing the cost and swapping it out as a test? Last point, make sure you've configured the module correctly in RSLogix 5000, and ensure it matches the physical arrangement in the rack, as you've suggested it might be a configuration issue. I hope this sheds some light and helps you get back on track.
Hey there! I've had my share of experiences with the 1794-VHSC module, as it can be quite finicky. Firstly, the wiring sounds alright to me - 0V to the A- terminal is the typical way to resolve the flashing A indicator. But you're right about the 24V A and A_ inputs that are often utilized for encoders. Your observation about the count rising even without flow hints at electrical noise, so it might be worth checking your shielding and grounding. As for your second inquiry, intermittent faults can be tricky. I've seen issues like yours before, and sometimes it's the result of a loose connector or an incorrectly set parameter within the module's configuration. Those status bits could also indicate an internal error. I suggest you to check the fault codes in the manual or consider replacing the module if the fault persists. Do remember to always keep your firmware up to date as well to avoid any compatibility issues! Let's keep digging to solve this mystery!
From my experience with the 1794-VHSC module, it does sound like a configuration problem you're facing. Ensure your wiring is correct; channel A should be wired to your pulse input, with the A- terminal going to your signal common or 0V reference if required. This might explain why your counts were increasing even without flow. As for the module faults, it might be related to configuration settings, not necessarily a hardware failure. You should review your scaling parameters -- sometimes, incorrect setup can cause counts to exceed the expected values. In addition, please check the update frequency of your logic’s scan rate. If it’s set too high (faster scan time), it might miss some counts. Lastly, regarding the status bits like Status.1 and Status.15 being set to one, it could be due to the mismatch of status conditions in your PLC program vis-a-vis module configuration. I hope you manage to resolve the issue soon, keep us updated!
Hey there! I won't claim to be an expert on the 1794-VHSC module, but from what I've witnessed dealing with similar setups, flashing indicators usually point to programming or electrical mismatches. Make sure you're carrying out the correct configuration on the PLC software end. You may want to try connecting your A input to pulse output and A- to 0V. This often works because most pulse outputs are Open Collector type, meaning it will sink your current back to 0V when the pulse is active. As for the spontaneous module flashing, if you can rule out hardware failure, it might be due to electrical noise or a possible grounding issue. Again, I don't specifically know the 1794-VHSC module, so it's best to consult someone with direct experience with it. Good luck with your troubleshooting!
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Answer: 1. How should the 1794-VHSC Pulse Counter Module be wired for proper functionality? - The A indicator should be flashing when the module is counting pulses. If this is not happening, ensure that 0V is connected to the A- terminal. This reference connection may be necessary for correct operation.
Answer: - The A and A_ inputs on the module are 24V, which might be intended for an encoder setup. For proper functioning, it is advised to have a 0V reference connected. Verify the wiring and make sure the connections are correct.
Answer: - If the module starts flashing and disrupts pulse capture, check the power supply, ensure it is not in PROG mode, and verify network connections. Additionally, monitor status bits like Status.1 and Status.15 for any anomalies that might indicate a fault in the module's operation.
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