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Dynamically changing an analog input to voltage or current

Created by: PLCAlex at: 6/12/2020 6:27 PM (8 Replies)

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6/12/2020 6:27 PM	Rate (0)
PLCAlex Experienced Member Joined: 4/14/2017 Last visit: 5/8/2023 Posts: 20 Rating: (0)	Hello to all of the wonderful Siemens gurus out there! I am using a SM1231 AI8 card on a 1214C system and was wondering is there a way to dynamically change the Measurement type from Current (4-20ma) to Voltage (0-10VDC) on a channel during runtime? Thanks, Alex
	Last edited by: PLCAlex at: 06/12/2020 18:31:33
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6/12/2020 6:49 PM	Rate (0)
LarryAm Silver Member Joined: 9/19/2011 Last visit: 1/17/2025 Posts: 140 Rating: (33)	PLCAlex Hello to all of the wonderful Siemens gurus out there! I am using a SM1231 AI8 card on a 1214C system and was wondering is there a way to dynamically change the Measurement type from Current (4-20ma) to Voltage (0-10VDC) on a channel during runtime? Thanks, Alex Hello Alex, The only way to change the measurement type from Current to Voltage is by downloading a new configuration to the PLC. Larry

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6/12/2020 6:59 PM	Rate (0)
Duris_I Diamond Member Joined: 4/28/2015 Last visit: 1/18/2025 Posts: 10753 Rating: (835)	Hello, sry but I'm very curious what is reason ask for that change in runtime. Can you be kind explain that?
	With best regards... Ivan Duris Flight: OMICO
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6/12/2020 7:02 PM	Rate (1)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 12/24/2024 Posts: 5014 Rating: (1026)	LarryAm PLCAlex Hello to all of the wonderful Siemens gurus out there! I am using a SM1231 AI8 card on a 1214C system and was wondering is there a way to dynamically change the Measurement type from Current (4-20ma) to Voltage (0-10VDC) on a channel during runtime? Thanks, Alex Hello Alex, The only way to change the measurement type from Current to Voltage is by downloading a new configuration to the PLC. Larry Though you are correct, there is a workaround that can be considered. _{(Only recently an old topic was re-opened which presents the idea.)}Option handling can be done. See: https://support.industry.siemens.com/cs/document/29430270/ The idea is to preconfigure hardware configurations that would possibly be used. The PLC will then boot up to the appropriate hardware configuration option. This is an option with limitations, but it can work. The alternative is to use external signal converters. It make the system more expensive BUT they can be made configurable and the PLC is isolated from the field (!).
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6/12/2020 7:14 PM	Rate (0)
PLCAlex Experienced Member Joined: 4/14/2017 Last visit: 5/8/2023 Posts: 20 Rating: (0)	Hi, The machine is a mobile piece of equipment and reads in a signal from the customer. Sometimes it is 4-20mA , other times it is a voltage signal. We use signal converters currently. I was just wondering if there was any unique solution to this. Thanks
	Last edited by: PLCAlex at: 06/12/2020 19:16:41
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6/12/2020 7:34 PM	Rate (1)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 12/24/2024 Posts: 5014 Rating: (1026)	PLCAlex Hi, The machine is a mobile piece of equipment and reads in a signal from the customer. Sometimes it is 4-20mA , other times it is a voltage signal. We use signal converters currently. I was just wondering if there was any unique solution to this. Thanks Hello. I think the option you have now has advantages that you should not overlook. Isolating the PLC to the field is good to have for a mobile machine. You can have two converters connect to each analog input through a relay if you wish to make the selection easy for the user. I think the cost can be well motivated. I had issues with a client not supplying the correct signalling as agreed on. I had to wire the signal to a variable speed drive. The drive in turn communicated with the PLC. The analog did not control anything in the drive. ... think of this technique if it would be helpful. Many drives has analog voltage and current inputs which can be reconfigured by communication.
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6/15/2020 1:38 PM	Rate (0)
LarryAm Silver Member Joined: 9/19/2011 Last visit: 1/17/2025 Posts: 140 Rating: (33)	qwazee LarryAm PLCAlex Hello to all of the wonderful Siemens gurus out there! I am using a SM1231 AI8 card on a 1214C system and was wondering is there a way to dynamically change the Measurement type from Current (4-20ma) to Voltage (0-10VDC) on a channel during runtime? Thanks, Alex Hello Alex, The only way to change the measurement type from Current to Voltage is by downloading a new configuration to the PLC. Larry Though you are correct, there is a workaround that can be considered. _{(Only recently an old topic was re-opened which presents the idea.)}Option handling can be done. See: https://support.industry.siemens.com/cs/document/29430270/ The idea is to preconfigure hardware configurations that would possibly be used. The PLC will then boot up to the appropriate hardware configuration option. This is an option with limitations, but it can work. The alternative is to use external signal converters. It make the system more expensive BUT they can be made configurable and the PLC is isolated from the field (!). Hello Qwazee, I do not believe that S7-1200 system supports the configuration option listed in your link. Larry

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6/15/2020 1:44 PM	Rate (0)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 12/24/2024 Posts: 5014 Rating: (1026)	LarryAm Hello Qwazee, I do not believe that S7-1200 system supports the configuration option listed in your link. Larry Hi Larry. The S7-1200 does have configuration control. You may find the attached document of interest. It is an extract from the official S7-1200 manual. Regards. Attachment Extract-Configuration-Control.pdf (210 Downloads)
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6/15/2020 2:32 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 1/17/2025 Posts: 15541 Rating: (2465)	My suggested solution does not require fancy PLC programming and configuration, is easy to explain to technicians, customers, and end-users, and easy to manage. It is not perfect, but it does work very well in situations like yours. Require the use a robust connectors on field devices. Configure the PLC for 0-10VDC (or +/- 10VDC) as the analog input allows. In the connectors for mA field devices, insert a resistor across AI+ and AI- pins, again on the FIELD DEVICE connector. The PLC side of the connector has no resistor. In this way, 0-10V signals connect up directly without a resistor and just work, and mA signals get converted to voltage. On the HMI enable dynamic calibration, and PLC logic requires calibration anytime a connector has been disconnected. You can cheat this - if the end-user is unreliable at performing calibrations and to ensure proper signal quality - by having 2 extra pins on the connector, and always jumper those pins on the field side of the connector. Run that from 24V on one pin, and digital input on the other side. Then you know when 24V is not available or the connector is disconnected. Often the signal coming in from a floating analog input is easy to detect, but if it is not, the extra pins option works quite well.
	science guy
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