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Pepperl+Fuchs Blog

Industrial RFID: UHF Parameters Revealed

Posted by Tim Cicerchi on Wed, Jan 21, 2015

A UHF RFID system is a bit more more complicated to configure and set up than an inductive short-range RFID system.  The Pepperl+Fuchs IUH-F190-V1-FR2-02 read head is a UHF head that makes many of the tough decisions for you.  You don’t need to know about anti-collision algorithms, sessions, inventory queries, or select flags.  We use simple concepts and a reduced parameter list to make it easy for anyone to set up an RFID system.

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RFIDControl software is a free downloadable program for configuring a UHF read head.  Many people ultimately decide to completely parameterize the reader in the PLC—which is the best decision, I agree. But you need to know what the parameters are in the first place to set them.  Use this software to easily try new UHF parameter combinations, and then activate the read commands to see how you did.

Initializing and opening the parameter window

Once the software is initialized, you will see the model numbers of both the connected controller and read head above and below the pictures.  If these are not there, then there has been an initialization problem and you should check your Ethernet or serial communication settings.  Once initialized, you will see a little box to the right of the picture of the UHF head.

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Figure 1: UHF parameter configuration box

Parameter descriptions

Once you click on the box, a list of parameters appears.  All parameters in the various fields are the actual parameters read from the F190 read head.  If you would like, click on the “Reset to factory settings” box at the bottom of the window to return the parameters to their default values.  Some parameters will be grayed out.  These are country-specific parameters that are not applicable for your setup.  For example, the Transmission Channels (CD) parameter is used only in countries that follow the ETSI standard.  North America uses FHSS, so no transmission channels can be specified.

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Figure 2: Parameter selection

Parameter Descriptions

Polarization (AP)

All of the RFID tags we sell are linear polarized.  You must either align the polarization plane of the reader to the tag or make the reader circular polarized.  If you don’t know the orientation of the tag, then circular polarization is a must.  Pepperl+Fuchs is one of the only companies that allows you to change the polarization of the reader.  If the orientation of the tags is known, changing the polarization to linear can give you 20 % more read range.  The selection options here are:

[ ]  Linear Vertical (V) – Tags are only read in a vertical orientation to the reader
[ ]  Linear Horizontal (H) – Tags are only read in a horizontal orientation to the reader
[ ] Circular (R) – Tags can be read in any orientation

Transmit Power (PT)

Power is an important parameter because the UHF transponder needs power to activate and enough power to respond to the command sent by the reader.  If the power is not high enough, then no communication takes place.  However, don’t make the power higher than necessary.  If you make the power too high, then you risk reading unwanted tags in adjacent read zones.  Often it is important to read the tag right in front of the reader and not ones 2 m left or right.  I always start at the lowest power settings and work up from there.  Up to 10 power values can be entered.  If more than one is entered, then all power settings are tried in sequence to read as many tags as possible.  Only certain discrete power values are allowed by the amplifier.  Even though any power setting is accepted from the minimum to the maximum, the power is always rounded down to these discrete power values listed below. The power options for the USA F190 reader are:

50 mW, 60 mW, 80 mW, 100 mW, 125 mW, 150 mW, 200 mW, 250 mW, 300 mW, 400 mW, 500 mW, default 125 mW – Transmit Power

Number of Channels (NC)

In North America, the use of the frequencies for UHF RFID communication is regulated such that you must use all 50 channels numbered 1-50 and you must use FHSS.  You have no control over which frequencies to use because the reader is always jumping around randomly.  The idea is that if one frequency is blocked, then no big deal, the next one you jump to may be open.  This parameter specifies how many frequencies are jumped to during one read cycle.  This parameter only has an effect on single read commands where a certain amount of time is spent trying to read tags in front of the reader before it stops.  The higher the number, the more reliable the read will be, but the longer the read will take.

1…50 – Number of channels to use during one read cycle, default 4

Number of Attempts (TA)

During a single read command, the F190 reader will try and read as many tags as possible until the read is done or the cancellation criteria is met.  Increasing the number of read attempts will make the reading more reliable but will extend the read time.

1…255 – Number of read attempts

Enhanced Status 5 (E5)

If a tag travels through the read zone on the fly, there is a possibility that it will go through small weak spots in the read field.  This would cause a status 5 or “no tag present” being sent to the user.  If it then travels into a part of the field that is strong, you would get the “Tag present” flag.  This parameter is basically an OFF delay filter.  The E5 parameter specifies how many read cycles the tag should not appear in before the “Tag not present” flag is raised.  This is an extremely important parameter for setup.  During install, I always set this parameter to 0 and then start an enhanced (continuous) read command.  I start then by putting the power at the lowest setting of 50 mW.  I look at the LED.  If the read LED is on solid when the tag is in the correct position and off when the tag is out of the read zone, then I know the setup is good.  If the read LED is blinking, I reposition the head and/or increase the power.  If this parameter is too high, it smooths out the blink of the LED and makes it more difficult to figure out if the power is correctly set or not.

0…252 – Cycles until a status 5 or a “Tag not present” is sent for a particular EPC/UII code

Memory Bank (MB)

Our commands SR, SW, ER, and EW stand for single read, single write, enhanced read, and enhanced write.  These commands are designed to read the read/write portion of a UHF tag.  Unlike LF and HF RFID tags, there is more than one read/write portion on the tag.  Each memory area is called a bank.  This parameter adjusts what memory bank the SR, SW, ER, and EW act on.

[ ] Bank 0 – Kill password and access password
[ ] Bank 1 – EPC/UII read/write area but must be unique for all tags in read zone
[ ] Bank 2 – TID, Fixcode or read-only number that the tags often use as a unique license plate
[ ] Bank 3 – (default) Read/write user memory

Protocol Mode (QV)

In order to read multiple tags in field at the same time, Pepperl+Fuchs extended their easy-to-use communication protocol.  This new protocol called Multi-frame can now accept 40 tags in response to a single command.  Certain applications utilizing only one tag in field can elect to continue to use the single-frame protocol.   This protocol mimics the responses of all the existing short-range RFID systems we sell and makes a long-range solution a drop-in replacement for a short-range one.  You can pick whichever protocol best fits your application needs.

[ ] Single Frame protocol (S) – Legacy protocol that lets the F190 mimic the LF or HF readers (1 tag in field max).  If multiple tags are in the field, data is replaced by a single status A error.
[ ] Multi-frame (M) – New protocol allowing for up to 40 tags to be read at one time, which may include additional information (default)

Additional Information (IF)

With each RFID tag, additional information can be provided.  This information can include the frequency the tag was read at, power value, and RSSI.  The frequency isn’t that important in the USA because you can’t change it, but in many countries one or a few frequencies are selected.  If you know all reads are occurring on only one of a few different frequencies, then those unused frequencies may be blocked by other readers.  The power value can tell you relatively how far away a tag is.  If one tag can be read at 50 mW and another can only be read at 150 mW, then the tag read at 150 mW is either farther away, being obstructed, or a relatively weak tag.

[ ] 0 = No additional information (default)
[ ] 1 = Additional information provided with each tag

Q Value (QW)

UHF tags use the ALOHA principle for collision avoidance. The reality is that only one tag can talk to the reader at a time.  In order to do this, the tags randomly pick a time slot.  The number of time slots is defined as 2Q.  More time slots mean the reading will take longer, but also that there is less chance that two tags will have a data collision and talk at the same time.  If there is a data collision, the inventory round is restarted with a new slot number being provided to the affected tags.  Reading is repeated until no more responses are heard from tags in the field.  The value of 2Q approximates the number of tags in the field.

[ ] 0 – Expect 1 tag in field
[ ] 1 – Expect 2 tags in field
[ ] 2 – Expect 4 tags in field
[ ] 3 – Expect 8 tags in field
[ ] 4 – Expect 16 tags in field
[ ] 5 – Expect 32 tags in field
[ ] 6 – Expect 64 tags in field (The F190 can read 40 tags in field max)
[ ] 7 – Expect 128 tags in field (The F190 can read 40 tags in field max)

Cancellation Criteria for Search (NT)

A single command is one that executes one time and then stops.  If you issue a single read or write command, you can specify the number of expected tags in the field.  The NT parameter when set properly will make the command execute as quickly as possible.  There is no reason to continue reading tags if you have already read them all.  Please note this parameter does not guarantee that you get exactly this many tags.  It just allows the read to stop early if the limit is reached.  The read can complete with fewer tags than expected. Or, it can respond to you with more tags than the limit, in the case where there are more tags in the field than you normally would expect.

[ ] 1…254 – In Single mode, it stops reading/writing when this threshold is reached
[ ] 255 – Disabled, it reads until the read cycle is complete

Transmission Pause (SM)

The F190 reader can operate and read tags continuously up to 50 °C.  If you add transmission pauses between read cycles, you can use the read head up to 70 °C.  This means that the F190 has the highest temperature rating in the industry.  These short pauses between reads allow the reader to cool down so the reader doesn’t overheat.

[ ] 0 – Read continuous
[ ] 1 – 65535 – Time in milliseconds to pause between read cycles

Real world setup

Even this small list of parameters may make setting up the F190 a daunting task.  Try and follow these steps to get your system best configured.  There aren’t as many parameters to set as you think.  Most you can just leave at the default.

1. Set the Power (PT) to 50 mW and the Enhanced Status 5 (E5) to 0.

2. Enable Enhanced read mode and click “Read”.

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Figure 3: Enabling enhanced read mode

3. Put one tag, mounted on the product you want to identify, in front of the reader.  Make sure the reader is facing the tag.  Check the READ/WRITE LED.  Is it reading and is the LED on solid?

4. If the READ/WRITE LED is on solid, your power adjustments are done.  If the LED is blinking, increase the power until the LED is on solid.  You may also have to reposition the read head to get better results.  Once the LED is on solid, your power adjustments are done, but make sure that the reader can’t pick up tags in adjacent zones.

5. You can make the reading more reliable by increasing NC, TA.

6. Change the E5 parameter back to 5 or a reasonable filter number.

7. Change the Q value to a number based on how many tags you have in the field 1 = 2 tags, 2 = 4 tags, 3 = 8 tags, 4 = 16…

8. Change the Cancellation Criteria for Search to the number of tags you expect to have in the field.  If you don’t know, set it to 255.

9. If you see that sometimes not all tags are being read, put in a power sweep.  Put a few additional power values in for the reader to cycle through.  Some tags may be weaker than others.  This will also compensate for obstructions and inconsistent mounting.

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Topics: Troubleshooting, RFID, Software

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