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Timing Critical Wireless System

Hi

I just need an advice on a possible wireless solution for my system.

My task is to collect responses from test-subjects in medical research
studies. This is done with different response pads with push-buttons.
Since the test subject is inside a scanner during the examination it
would be practical to have battery driven response pads with a
wireless transmission solution instead of cabling.

But my biggest problem with such a solution I guess is the timing
issue because timing in these studies are often critical, and
deviation in the delay from one response to the other more than a
10-100 ms caused by signal delay in the system is not accepted.

Does anyone have a suggestion on a ready to use solution for such a
timing critical wireless system?

-Transmission length is maximum 7-10 meters (30 feet???) from sender
to receiver
-This is inside a faradays cage, meaning little RF noise in the room,
but for regulative reasons only the common used frequency bands
(open) should be used.
-Up to 3-4 independent transmitters should be able to work with the
receiver simultaneously

My idea is that some alarm systems probably are wireless with strict
requirements, and not to forget high-end gaming devices that use a
wirless solution (if that excist...)

I'm greatful for any suggestions or advice.

Stian SS
 
D

Donald

Jan 1, 1970
0
Hi

I just need an advice on a possible wireless solution for my system.

My task is to collect responses from test-subjects in medical research
studies. This is done with different response pads with push-buttons.
Since the test subject is inside a scanner during the examination it

Whats the scanner ?
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
Hi

I just need an advice on a possible wireless solution for my system.

My task is to collect responses from test-subjects in medical research
studies. This is done with different response pads with push-buttons.
Since the test subject is inside a scanner during the examination it
would be practical to have battery driven response pads with a
wireless transmission solution instead of cabling.

But my biggest problem with such a solution I guess is the timing
issue because timing in these studies are often critical, and
deviation in the delay from one response to the other more than a
10-100 ms caused by signal delay in the system is not accepted.

Does anyone have a suggestion on a ready to use solution for such a
timing critical wireless system?

-Transmission length is maximum 7-10 meters (30 feet???) from sender
to receiver
-This is inside a faradays cage, meaning little RF noise in the room,
but for regulative reasons only the common used frequency bands
(open) should be used.
-Up to 3-4 independent transmitters should be able to work with the
receiver simultaneously

My idea is that some alarm systems probably are wireless with strict
requirements, and not to forget high-end gaming devices that use a
wirless solution (if that excist...)

I'm greatful for any suggestions or advice.

Stian SS

An RF solution shouldn't have too much trouble with the latency
requirements. The Faraday cage and scanner make me think that avoiding
interference with the equipment might be your biggest problem. Have you
considered an IR link?

--
Paul Hovnanian mailto:p[email protected]
------------------------------------------------------------------
The opinions stated herein are the sole property of the author. All
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and consult a physician.
 
Again - what type of scanner?

The shielding strongly suggests an MRI scanner, in which case the
problem will not just be rf interference with the scanner.

Two other problems will be:

1) The scanner transmits very high power pulses of rf whiich could
have a bad effect on your circuit.

2) There will be a VERY powerful magnetic field which can easily turn
seemingly harmless items such as batteries with steel casings into
dangerous projectiles.

You would be better off using a fibre-optic system where the button
interrupts the light path between two optical fibres. All electrical
and electronic components could then be outside the shielded
enclosure.

Alternatively, thin plastic tubes and a pneumatic bulb under each
button and a pressure switch at the other end could work.

John
 
M

MooseFET

Jan 1, 1970
0
Hi

I just need an advice on a possible wireless solution for my system.

My task is to collect responses from test-subjects in medical research
studies. This is done with different response pads with push-buttons.
Since the test subject is inside a scanner during the examination it
would be practical to have battery driven response pads with a
wireless transmission solution instead of cabling.

But my biggest problem with such a solution I guess is the timing
issue because timing in these studies are often critical, and
deviation in the delay from one response to the other more than a
10-100 ms caused by signal delay in the system is not accepted.

Do you need to react quickly or merely know exactly when the pad was
pressed? You can have the circuit that it connected to the button
have an internal clock that it records at the instant of the press.
 
Hi

I just need an advice on a possible wireless solution for my system.

My task is to collect responses from test-subjects in medical research
studies. This is done with different response pads with push-buttons.
Since the test subject is inside a scanner during the examination it
would be practical to have battery driven response pads with a
wireless transmission solution instead of cabling.

But my biggest problem with such a solution I guess is the timing
issue because timing in these studies are often critical, and
deviation in the delay from one response to the other more than a
10-100 ms caused by signal delay in the system is not accepted.

Does anyone have a suggestion on a ready to use solution for such a
timing critical wireless system?

-Transmission length is maximum 7-10 meters (30 feet???) from sender
to receiver
-This is inside a faradays cage, meaning little RF noise in the room,
but for regulative reasons only the common used frequency bands
(open) should be used.
-Up to 3-4 independent transmitters should be able to work with the
receiver simultaneously

My idea is that some alarm systems probably are wireless with strict
requirements, and not to forget high-end gaming devices that use a
wirless solution (if that excist...)

I'm greatful for any suggestions or advice.

Stian SS

Yes we are talking about an MRI scanner here, but to answer your
questions:

1: The response pads will be at the subjects hands, meaning outside
the MR-bore not not so much affected by the shifting gradients and RF
transponders - but it's not unusual to have electronics like LCD
projectors/displays etc. located insider the bore mounted to he RF
transponder coil.

2: The RF interference of the scanner is in the frequency range 60 Mhz
and 120 Mhz, if we're going for a solution outside the frequencies RF
interference should not be a to big problem.

So do anyone have any experience with wireless system with minimum
latency?

Thanks in advance!
 
W

whit3rd

Jan 1, 1970
0
How about TV remote controls? There's lots of handheld controllers
to choose from, the number of available buttons is adequate,
and receivers for computer (or other) connection are common
enough; see www.lirc.org for more info.
 
J

joseph2k

Jan 1, 1970
0
whit3rd said:
How about TV remote controls? There's lots of handheld controllers
to choose from, the number of available buttons is adequate,
and receivers for computer (or other) connection are common
enough; see www.lirc.org for more info.
Possible but also maybe not suitable due to EMC and high magnetic field
compatability. Proper engineering should recommend a technology compatible
with any type of medical scanner.
Since controlled and preferably low latency is requires reliable detection
with sub-millisecond total response time. This leads to continuous
transmission at 10,000 symbols per second through the "push button" and a
sturdy, reliable, low required force mechanism no matter how done. After
that, RF, IR, and visible light are all reasonable choices. Air (or other
fluids) will not be fast enough. The fiber interrupter looks like the best
bet, followed by (perhaps moving mirror) free path optic interrupter (no
wires of any kind, but much harder to setup and has other usage problems).
 
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