Site Information – Using RF Wrench Issue A 5th May 2011 The following information should act as guidelines to ensure the RF system works reliably: 1.
Before using the RF system it is worthwhile checking the following is true: •
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2.
Both the wrenches and receiver are set up to the same frequency channel; otherwise communication may not occur. Typically: o Channel 25 is used in USA o Channel 64 is used in Europe That the receiver has been paired with the wrenches that it has to work with, otherwise it will see the wrenches are present but will not attempt to receive or transmit data packets with them. That the correct antenna has been fitted to the receiver to match with the frequency channel being used. Typically: o Channel 25 will have antenna with yellow band o Channel 64 will have antenna with grey band. Ensure that the antenna is finger tight into its connector (i.e. not loose, yet not over-tightened). This is because if there is an intermittent connection between the receiver and its antenna, then the signal reception will be reduced which could reduce the range. Wrench
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It is recommended that the wrench should be used no more than 10m from the receiver. The wrench may be found to work further than 10m but the received signal strength will be lower and therefore make the link more prone to external noise and interference. This may make it take longer for the information to be transferred as several retries are required or that no communication is possible. To ensure a reliable link we have set a limit of 80dBm for the received signal on the wrench.
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3.
The wrench checks its received signal before it transmits and if it is below -80dBm it will display that the “Wrench is out of range” and will not attempt to transmit. In this situation, the user should bring the wrench closer to the receiver as this will increase the received signal strength and the wrench can then be asked to re-try sending the data. At this stage the wrench is checking that the received signal strength is greater than -70dBm. The orientation of the wrench can affect the signal reception. If one finds that in one orientation the reception appears low, just changing the orientation of the wrench may improve the reception. RF theory shows that if the wrench is parallel (the length of the wrench is in same direction as receiver antenna is pointing, then the signal will improve). For the suggestions of positioning the receiver below, this would mean holding the wrench vertically. Similarly if the wrench is pointing towards the receiver, then signal will be decreased. This is theory and in practice, due to reflections off nearby structures, one may find other orientations that reduce the signal reception. Putting a hand around the display part of housing could potentially reduce the signal strength. This is because body tissue can attenuate signal. Placing the wrench on metal surface can attenuate signal. An example, of this, is if the wrench is put into its cradle, then the signal will be reduced because the cradle back plate is made of metal (aluminium). RF Receiver
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It should be at a height of 1.6 to 2.0m
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Its antenna should be pointing vertically upwards / downwards.
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If there is metal present the antenna should be pointing away from the metal as the ground effect can help the signal
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The antenna should not be parallel and close to metal as this will reduce the signal. Interference The following issues may cause a problem with interference which would reduce the RF range or stop communication altogether.
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Metal structures in between the wrench and the receiver will absorb or reflect the RF. This may cause local black spots and if the wrench is moved a small distance, the reception would get better.
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Welding nearby will give a broadband noise source. Certain Mobile phones that operate in 900 – 1000MHz region can saturate the RF signal. It is already known that mobiles can affect other electronic equipment in near vicinity. Some Radio systems use 433MHz and the 2nd harmonic (which is normally low) could interfere. If radio systems are being used to communicate with operators or pieces of equipment in local vicinity that a note of their frequency is recorded and Crane informed.
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There are other electrical and electronic equipment that could be present and at present we are not aware of it causing a problem: • • • •
Wifi / Bluetooth / Zigbee systems that use 2.45GHz should pose no problem as narrow band and higher frequency. CB Radio at 27MHz should pose no problem as low frequency Fluorescent light tubes should pose no problem as give low frequency noise. Motors with carbon brushes should pose no problem as will mainly generate low frequency noise.
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Testing environment
5.1
The reception on the wrench can be tested in 2 ways:
5.1.1 Directly on wrench • In wrench Setup / Comms Setup / RF Comms / RF State can get the following information on wrench screen, each time press green button. • Will get STATE a b/c d e reported back where: o a: 1/0: Connection to RF Receiver OK / NOK (connection-ok-flag) o b: Number of datapackets in TX queue o c: Size of TX queue o d: RSSI [dBm] possible values: -46, -48,… .,-106, -108 o e: Status word (16 bit hexadecimal): • Look at ‘a’, which should be 1. If 1, then can use figure ‘d’ which represents the received signal strength. Ideally the signal strength should be between 48dBm (when wrench very close to receiver) and -68dBm 5.1.2 Indirectly via RF Receiver • If talk to the receiver using Hyperterminal can use following commands to get the signal strength being received by the wrench. • Assuming that the RF ID for the wrench is xx. o >xx login 4 123 o xx> Hi! o >xx ?state // Can be repeated. o xx> STATE a b/c d e • The same criteria apply as in 5.1.1 with the bonus that if the wrench reception is too low, then will not get a response to command. 5.1.3 RF Receiver • The signal received at the Receiver can be shown using the following command: o login 4 123 o Hi! o ?fsh all o xx 80 1 0 -48 0010 o xy 80 0 8 -50 0010 o <Addr> <Type> <Log> <Time> <RSSI> <Status> <Addr>: Device address <Type>: Device type <Log>: 0/1: logged OUT / in <Time>: Time since last contact (0 ,8 ,16s or “-“) <RSSI>: RSSI value at the last contact <Status>: 16 bit status flags of the wrench • The same criteria apply as in 5.1.1 in that the RSSI should be between 48dBm and -68dBm. Neil McDonald