LVDT Signal Conditioning FAQ

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LVDT Signal Conditioning

 

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How do I use the RS-485 Port of your LVDT Signal Conditioners?

Using the RS-485 port of ASG S2A/SC-200 LVDT signal conditioners   Aug 1, 2019

 

ASG's LVDT signal conditioners incorporate an RS-485 two-wire multi-drop serial communications interface for up to 16 devices. This port enables half-duplex serial communication by which a module can be set up and calibrated remotely and system data can be read or stored on a PC running an ASCII terminal program like Hyper Terminal with a 2-wire RS-485 converter for the computer's com port or USB port connected to terminals J3-1 and J3-2 of the signal conditioner. The PC's com port parameters are: 9600 bps, no parity, 8 data bits, and 1 stop bit (9600, NP, 8, 1), with echo on and no flow control. Be sure that the RS-485 connection for Data A (D-) is connected to J3-2 and Data B (D+) is connected to J3-1. Always follow the data polarity (D) indicated above, regardless of the letters for data lines used by the RS-485 converter.

 

ASG offers a 1.8 m long 2-wire USB-to-RS-485 converter cable, USB-RS485-WE, p/n 5810-0001, having an orange wire with a red tip plug that is Data B (D+), and a yellow wire and tip plug that is Data A (D-). Normally no driver is needed for a USB-RS485-WE used with MS Windows 7 or later. For Windows XP or earlier, or MAC or Linux operating systems, driver software can be found on: www.ftdichip.com. In most cases, the optimum driver for any particular OS is the VCP version.

 

RS-485 user commands for S2A/SC-200 ASG LVDT signal conditioner modules

 

Note that all commands must be formatted to begin with UXX followed by a space, where XX is the numerical value between 00 and 15 of the module's decimal digital address as set up on DS2, switches 5, 6, 7, and 8 according to Table 1b in the S2A instruction manual, or by following the DIP switch settings diagram shown on the S2A module's left side label.

 

Note: Some Set command descriptions show in bold face the range of values that follow the command and a (space).

 

Analog In RUN mode, returns the nominal analog output value scaled in electrical units that depend on the setting of DS1, or the analog output range selected with the Set Aout command.

 

Cal Enters CALIBRATION mode; command is the same as pressing FULL SCALE and ZERO pushbuttons together.

 

Clrall In RUN mode, clears EEPROM of all RS-485 command settings used to override module's DIP switch settings. 

 

Config Lists the module's setup data and displays DIP switch settings and current EEPROM values. Specifically, it shows the module's firmware version, operating mode, digital address (00 - 15), date stamp, serial number, analog output setting (1 - 8), excitation frequency setting (0 - 3), output invert switch off or on, low frequency filter status (LF) off or on and filter corner frequency, excitation drive jumper (J7) in or out, failure output delay time (FD) and polarity (FOP) NC or NO, Lock status, and stored EEPROM values for ADC Lo, ADC Hi, Input pot, and Gain pot.  (Log and store all Config data and values by digital address to be able to reconfigure a hot swapped module at a later time).

 

Error In RUN mode, displays any setup or operations error code(s); for multiple errors, the error code sum is displayed.

 

Errsec In RUN mode, ON, OFF (default) toggles error indications and failure outputs from low DCR LVDT secondaries.

 

Errsig In RUN mode, ON (default), OFF toggles error indications and failure outputs for all errors found during setup.

 

Exit Required to exit CAL mode, or to exit any Set command writing a value to the module's EEPROM in RUN mode.

 

FS In CAL mode, sets the module's full scale output point at the LVDT core’s maximum position and is the same as pressing FULL SCALE pushbutton. Occasionally it may require setting a second time after using the Z command.

 

Help Shows all ASCII user commands available for execution over the RS-485 bus, including a few not shown in this list.

 

LEDs In RUN and CAL modes, outputs the status of the 3 green LEDs, displayed in S-E-P order, e.g.:  - * 0  means S LED is off, E LED is flashing slow, and P LED is on. + is a fast flash and ! indicates alternating solid and flashing.

 

Lock In RUN mode, locks the module against any changes and displays attempted tampering over the RS-485 bus.

 

Null In RUN mode, displays the Null Output voltage at any core position and is typically used to verify that the core of an LVDT is at null; may also be used to establish the symmetry of an LVDT’s endpoint outputs versus core position.

 

Read LF In RUN mode, when DS2-4 is ON, or the LF filter is invoked, shows the status and frequency setting of the supplemental low frequency low pass filter.

 

Recal FS In RUN mode, after a calibration has been completed, if the actual full scale output value is within ±4% of the nominal full scale output value selected by DS-1 or the Set Aout command, this command trims the actual full scale output value to match the selected full scale output value. The command may be repeated once to get the most precise FS output value. Recal can be set at module by pressing and holding the FULL SCALE button until the POWER LED blinks.

 

Recal Z In RUN mode, after a calibration has been completed, if the actual zero output value is within ±4% of the nominal zero output value selected by DS-1 or the Set Aout command, this command trims the actual zero output value to match the selected zero output value. This command may be repeated once to get the most precise zero output value. Recal can also be set at the module by pressing and holding the ZERO pushbutton until the POWER LED blinks.

 

Reset In RUN mode, produces a "soft" reset of the module's processor so the module restarts as if it is powering on. Command is the same as pressing the FULL SCALE pushbutton three times for at least one-half of a second each.

 

Reset All In RUN mode, using prefix U90 instead of Uxx, this command performs a simultaneous "soft" reset on all modules connected to the RS-485 bus.  Each module on the RS-485 bus then restarts itself as if it is powering on.

 

Restore In RUN mode, resets module to factory set condition by cancelling all user setup values stored in EEPROM. It can also be invoked by pressing the ZERO pushbutton three times in a row for one-half of a second each time.

 

Set ADC Hi In RUN mode, writes an A/D converter high value into module's EEPROM. Command is used during a hot swap module reconfiguration to enter the ADC Hi value logged from the original module's Config command.

 

Set ADC Lo In RUN mode, writes an A/D converter low value into module's EEPROM. Command is used during a hot swap module reconfiguration to enter the ADC Lo value logged from the original module's Config command. 

 

Set Aout In RUN mode, permits setting the analog output range: 1 - 8, independent of the setting of DIP switch DS1.

 

Set Exf In RUN mode, permits setting excitation frequency: 0 - 3, independent of settings of DIP switches DS2-1, -2.

 

Set FD In RUN mode, permits the user to set the delay time before the failure warning output switch is activated from 0 to 900 msec in 100 msec increments: 0 - 9. The factory default delay time is set at 200 msec.

 

Set FOP In RUN mode, sets failure warning switch polarity: NC, Normally Closed (default) or NO, Normally Open.

 

Set Gain In RUN mode, writes a Gain pot value into module's EEPROM. Command is used during a hot swap module reconfiguration to enter the Gain pot value logged from the original module's Config command. 

 

Set In Pot In RUN mode, writes an Input Pot value into module's EEPROM. Command is used during a hot swap module reconfiguration to enter the Input Pot value logged from the original module's Config command.

 

Set Inv In RUN mode, permits inverting analog output by overriding setting, ON, OFF, of invert DIP switch DS2-3.

 

Set LF In RUN mode, sets the corner frequency of the supplemental low pass filter between 0.1 Hz and 10 Hz. If DS2-4 is not ON, command permits LF filter status to be changed: ON, OFF, and its corner frequency to be set.

 

Ver In RUN mode, returns the version number of the module's firmware.

 

Z In CAL mode, sets the module's zero output point at the minimum position of the LVDT's core; function is the same as pressing the ZERO pushbutton. Occasionally it may require setting a second time after using the FS command.

 

 

 

Where can I find your LVDT S2A and SC-200 Graphic User Interface (GUI) Instructions?

Here's the Complete Graphic User Interface (GUI) Instructions:

1. Connect a 2-wire RS-485 port converter to the computer on which this GUI is to run and connect the converter's output terminals to the RS-485 bus connections on the LVDT module(s),  Data A (D-) connects to terminal J3-2 and Data B (D+) connects to terminal J3-1, but always follow the data polarity (D) indicated above, regardless of the letters used for the data lines.

2. Invoke the CONTROL PANEL program in the computer.  Open SYSTEM, then click on the HARDWARE tab and choose DEVICE MAMAGER.

3. Go to PORTS and identify the port number(s) associated with the available Com Port(s), i.e., Com1, Com2, etc. Note Com Port number(s) for later use in the GUI setup. Double click on COMMUNICATIONS PORT to see port properties. Click on PORT SETTINGS tab and verify that the port settings are: 9600 bps, 8 data bits, no parity, 1 stop bit, and no flow control.

4. Download executable file ASG SC100 GUI MNGR.EXE from ASG website and run it.

5. Open folder created by executable file above and run the program ASG_SC100MNGR.EXE.

6 After this program is loaded, a screen appears with several tabs on top.  Click on the SETUP tab. Enter the Com Port number noted in step 2 above in box at the top of the System Setup screen and click the APPLY button. This action will require restarting the program of step 5.

7. After the program restarts, click on FILE tab and then click on DISCOVER.  This will bring up the main GUI screen.  After discovery finishes, make certain the CURRENT SETTINGS for any particular digital address match how the DIP switches for the module with that address were setup. Enter the Device Name and Description into the appropriate labeling blocks as desired.

7a. If there was any communications problem, click the CHECK CONNECTIVITY button and verify that the version number returned matches that in the CURRENT SETTINGS box. If there is not a match or an error is reported, recheck the com port setup by repeating steps 1 to 3.

8. Click on the CALIBRATE button and follow the prompts in the screen box to calibrate the module to the range of core position or motion for the LVDT connected to that module. 

9. When the calibration is complete, click on the SCALE UNITS button and follow its prompts.

11. To display the module's output in both electrical and measurement units, click on the READ button.  For a continuous display of the readings, click the CONTINUOUS READ checkbox.

What are the differences between the S2A and SC-200 LVDT Signal Conditioners?

The S2A and SC-200 LVDT signal conditioners are very similar; however, each unit was designed with specific features for the markets it serves in mind, so there are a few differences between them.

The S2A was specifically designed for the power generation industry and has the following features:

  • LVDT excitation frequencies of 1, 3, 5, and 10kHz. The 1kHz and 3kHz frequencies were selected so the conditioner could be used with GE and Westinghouse steam turbine LVDTs and LVRTs.

  • If the S2A senses a sensor-related fault, the module's fault-response outputs are activated and in addition, the analog output is driven out of range. This is done so that in a redundant sensor configuration, by using an algorithm coded into the turbine's DCS control system, the faulty reading is identifiable and is not be accepted by the DCS with the other correct sensor readings.

  • The I/O screw-terminal plugs are color-coded and are removable for easy installation.

 

The SC-200 was designed for standard industrial applications and has the following features:

  • LVDT excitation frequencies of 2.5, 5, 7.5, and 10kHz. The 2.5kHz frequency is commonly used by LVDT manufacturers and the 7.5kHz frequency was selected to be used with Marposs analog pencil gaging probes. Alliance Sensors Group is an official distributor for Marposs USA.

  • The analog output is NOT driven out of range should the SC-200 sense a fault, but the module's other fault-response outputs are activated.

  • The I/O screw-terminal blocks are not removable.

 

 

 

Where can I find the LVDT Signal Conditioning Software Download?
How do I use the RESTORE Function for S2A or SC-200 LVDT Signal Conditioners?

An S2A or SC-200 module set for 4-20 mA output displays an output error during setup

1. Before taking any specific remedial action:
    a. Make sure that the analog output is not connected into a loop powered system.
    b. Make sure that there is a loop load resistor connected to the module's output terminals.
2. If the E and S LEDs are blinking and the P LED is not illuminated, perform the RESTORE function by depressing the front panel ZERO pushbutton 3 time in a row for a least 1/2 second duration each time.
3. If the RESTORE function was successful, the E and S LEDs will go off and the P LED may turn on. 
4. If the RESTORE function was unsuccessful, repeat the process, carefully observing the duration.
5. When successful, proceed to calibrating the module with the connected LVDT sensor normally.

What are the recommendations for DC power supplies and USB-based data acquisition hardware for use with ASG's signal conditioners and DC-operated sensors?

DC Power Supplies

There are two distinct types of DC power supplies that convert the AC power line voltage into DC voltage to operate electronic devices. Linear supplies use a transformer, rectifier diodes, a regulator, and filtering to produce relatively clean DC, but they are limited to a narrow range of power input voltages and are usually physically large. Switching supplies offer a wider range of power input voltages and are usually smaller in size, but often have switching frequency noise on their DC output. Both types are available in a variety of packages, but most DIN-rail-mounting units are switching supplies.

Because ASG's devices draw relatively low current, the chart of recommended power supplies shown below is based on the number of similar units being powered at the same time. All the power supplies listed below are available from national electronic component distributors such as Digi-Key, Mouser, Newark Electronics, or Allied Electronics at unit prices from $40 to $120. Output Number TDK Lambda Mounting Phoenix Contact Mounting ASG Product

Output Volts DC Number Devices TDK Lambda Part Number Mounting Phoenix Contact Part Number Mounting AFG Product Application
12 V 12 DSP10-12 DIN rail 2868538 DIN rail, tabs DCSE LVDT
15V 8 DSP10-15 DIN rail     MR, ME, LV LVIT
24 V 6 DSP10-24 DIN rail     LVIT, S2A, SC-200
24 V 10     2868535 DIN rail, tabs LVIT, S2A, SC-200
24 V 16 DSP30-24 DIN rail 2868648 DIN rail, tabs LVIT, S2A
24 V 16     2866446 DIN rail only S2A, SC-200

Data Acquisition Systems

For analog data acquisition (DAQ) input to a PC, the simplest products to utilize are generally USB-based instruments. There are several USB-DAQ choices offered by National Instruments (NI), or their subsidiary, Measurement Computing Corp. (MCC), (which offers more economical DAQ products) that work with ASG products. Typically, USB-based DAQ systems can operate from the 5-Volt DC power of a USB port, so an additional power supply is normally not needed. These DAQ systems work with all the popular NI software like LabVIEW and Signal Express.

DAQ systems are usually used with an analog voltage input, and the majority of ASG products offer a single-ended, ground-referenced DC voltage output up to 10 Volts full scale. Most DAQ systems have at least 8 single-ended analog inputs, and some have differential inputs as well. A DAQ with a differential input capability is of particular benefit for use with sensors that have their DC output off-ground, like some types of DC-LVDTs that offer either a 3-wire connection with a 1-6 Volt grounded output, or a 4-wire hook up with a 0-5 Volt output in which the return side of the output is floating 1 Volt above the ground of the sensor’s power supply.

Recommended USB DAQs for single-ended inputs are the MCC USB200 series and the NI USB-6000 series. Recommended USB DAQs for both single-ended and differential inputs are the MCC USB-1208 series and the NI USB-6008 series. All have a resolution of 12 bits, with a variety of sampling rates available. Detailed product information is available on the respective websites of the suppliers: mccdaq.com or ni.com.

How do I use the Restore function for the S2A or SC-200 Signal Conditioners?

An S2A or SC-200 module set for 4-20 mA output displays an output error during setup

 

1. Before taking any specific remedial action:

            a. Make sure that the analog output is not connected into a loop powered system.

            b. Make sure that there is a loop load resistor connected to the module's output terminals.

2. If the E and S LEDs are blinking and the P LED is not illuminated, perform the RESTORE function by depressing the front panel ZERO pushbutton 3 time in a row for a least 1/2 second duration each time.

3. If the RESTORE function was successful, the E and S LEDs will go off and the P LED may turn on.

4. If the RESTORE function was unsuccessful, repeat the process, carefully observing the duration.

5. When successful, proceed to calibrating the module with the connected LVDT sensor normally.