Application Notes - Reed Relays
High Voltage Reed Relays
The principal function of a high voltage reed relay is to isolate as high a
voltage as possible, Cynergy3 achieve this through the use of
evacuated reed switches. These are available with Tungsten or
Rhodium contacts, depending on the switching requirements of the
applications. These relays are intended for use in DC or AC (50Hz to
60Hz) applications.
RF Reed Relays
Cynergy3's range of RF reed relays are carefully designed to provide
minimal RF signal loss and low contact resistance. This is achieved
through the use of copper plated reed switches, with Rhodium
contacts, packaged in carefully designed coil assemblies. These
relays are designed for use in the HF band and are typically used in HF
amplifiers and aerial tuning units (ATU's). The standard performance
measure of an RF reed relay, adopted by Cynergy3, is Effective Series
Resistance (ESR); this is because these relays are very often used in
high “Q” circuits, which experience high currents throughout the
frequency range, as found in certain ATU circuits.
0 dB
-0.025 dB
-0.05 dB
Insertion loss
1 MHz
15 MHz 30 MHz
Return loss
Isolation
0 dB
50 dB
100 dB
Figure 1 : Typical Parameters of Cynergy3 RF Reed Relay
General
The following are some general guidelines, which should be considered
when working and designing with Cynergy3's range of reed relays. It
should be noted that all data is presented, throughout, at an assumed
ambient temperature of 20°C, unless otherwise stated.
COIL
Coil Temperature Compensation
Coil resistance, as well as 'Must Operate' & 'Must Release' voltages, is
quoted at 20°C, unless otherwise stated. It should be noted that these
parameters will change at a rate of 0.4% per °C change in
temperature.
Coil Suppression
It is recommended that all relay coils be suppressed, by fitting a
reverse biased diode across the relay coil; this is essential for latching
relay types. Operate and release times for the relays are quoted with
coil suppression fitted (unless otherwise stated).
Coil: RF Screening
The benefit of RF screening is that it reduces the RF through losses
(ESR) of the relay and extends the relay performance, at high
frequencies and high ambient temperatures.
The RF reed relays offered by Cynergy3 have various screening
options:
· Uns creened
· Partially S creened
· Fully S creened
Unscreened relays maybe used in RF circuits where the highest
currents occur at the lower frequency bands e.g. 2MHz.
Partially screened relays will offer extended current carry capability at
elevated temperatures and frequencies up to 30MHz, over unscreened
variants, due to lower ESR.
Fully screened relays offer the ultimate in low loss performance,
resulting in the lowest ESR figures, significantly reducing the effects of
RF coil heating, and maximising current carry performance at elevated
temperatures and frequencies.
Relay ESR Measured at 4.5A, 30MHz
160
140
120
100
80
60
ESR (mOhms)
40
20
0
FRD13000 Series
(Full Screen)
FRD12000 Series
(Part Screen)
FRD12000 Series
(No Screen)
Figure 2: Effects of screening on ESR
Coil: Magnetic Screening
A magnetic field is produced, when power is applied to the coil of a
reed relay. Ferromagnetic screening can be used to contain this
magnetic field, so allowing closer placement of reed relays on a PCB. It
should be noted that many of the RF relays do not employ magnetic
screening, as this can adversely affect the ESR; in this case refer to
figure 3, for a suitable layout for RF relays without magnetic screening.
1. Side by Side
2. As above but interleaved
Figure 3 : Mounting Configurations to Minimise Magnetic Interference (Note Orientation)
Figure 4 shows a suitable arrangement for 'D' & 'S' type high voltage
relays.
Note that the 'D' Series has magnetic screening fitted as standard.
? 5mm
DAT71210 XXXX
? 5 mm
DAT 71210 XX X X
DAT 71210 XX X X
DAT 71210 XX X X
Figure 4 : Recommended Mounting for "S" and "D" Series High Voltage Reed Relays
DAT 71210 XX XX
DAT 71210 XX XX
DAT 71210 XX XX
DAT 71210 XX XX
? 5mm
? 5mm
CONTACT
Contact Arrangements
SPNO (FORM A): Normally open - energise to close contacts
SPNC (FORM B): Normally closed – energise to open contacts
Latching: Contact is bistable – energise “SET” coil to close contacts;
energise “RESET” coil to open contacts.
Contact Isolation Voltage
The isolation voltages quoted in the data are for DC or AC peak. The
two may be considered directly equivalent, at mains frequency (i.e. 50
or 60Hz).
High voltage breakdown mechanisms at RF differ from those at DC. In
general breakdown across the contacts occurs at a higher RF peak
voltage than DC. Conversely, breakdown outside the switch (i.e. switch
to coil or screen), caused by surface tracking, can occur more readily at
high frequency than at DC. Verification of any particular voltage or
frequency combination, within the HF band (1–30MHz), can be
undertaken upon request.
Contact Switching Power
The switching power, when quoted, will be for a resistive load. It should
be noted that any combination of voltage and current can be switched,
provided they do not exceed the stated switching maximums, for either
parameter or the power rating of the contact. It should be noted that
relays, used in a power switching application, will experience reduced
operating life; it is recommended that sales be contacted for advice on
specific applications.
Contact Material – Rhodium vs Tungsten
Rhodium offers superior low contact resistance, which, coupled with
Cynergy3's copper plated reed switch technology, enables Cynergy3 to
produce very low loss RF reed relays, with exceptional current carry
performance. Rhodium contacts are offered, in our 'D' series range, for
high voltage applications, where low contact resistance and good
current carry performance are required, provided the switching voltage
is below 1000 volts DC or AC peak.
Tungsten contacts are used exclusively for our high voltage 'D' series
range, where they are offered as high voltage switching contact able to
switch voltages up to 10kV DC or AC peak at very low current.
Tungsten is a good general purpose switching contact material but the
higher contact resistance means it is not well suited for RF
applications.
PROCESSING & HANDLING
Cynergy3's reed relays are high performance products and the
materials and methods of construction are significant.
factors in achieving performance specifications. The following
guidelines should therefore be followed when adopting assembly,
soldering and cleaning processes.
Handling:
Many of the RF reed relay designs are of open frame construction to
achieve optimum RF performance, these designs need to be handled
with due care to avoid damaging the exposed coil, contact and screen
connections.
Soldering:
Cynergy3 recommend the following wave flow soldering profile:
250ºC ±10ºC, immersion time 3 seconds.
Alternatively, for manual soldering iron operations:
350ºC ±10ºC, application time 3 seconds.
Maximum exposure time 10 seconds.
Cynergy3 propose that either low residue fluxes are used in the
soldering process (to eliminate the need for cleaning), or that the reed
relays are fitted onto the PCB after the cleaning process has taken
place.
FRD12000/13000 Series: Electrical connections to the relay contacts
on the FRD12000/13000 Series relays are made directly onto the reed
switch leadout. Care must be taken when hand soldering to the
contact terminals, as physical and thermal shocks can damage the
glass to metal seals. It is recommended that a thermal shunt
(Aluminium Clamp) be clamped to the reed switch lead out adjacent to
the glass seal; this will reduce the chance of breakages due to thermal
shocks. Alternatively relays may be warmed prior to soldering.
Cleaning:
Cynergy3 relays are not hermetically sealed (unless stated otherwise)
and as such are not suitable to aqueous cleaning solutions or
processes. If after the soldering process the customer wishes to clean
the PCB's containing Cynergy3 relays then the use of post operative
cleaners such as IPA or HCFC based solvents with low pressure brush
applicators is recommended. Please contact sales for further
information on the suitability of various cleaning solutions.
ENVIRONMENTAL ENDURANCE
Many of the designs manufactured by Cynergy3 Components Ltd are
used in Military and Defence systems therefore many of the relay
designs have been tested for Bump, Shock and Vibration endurance to
the following standards:-
Bump Test: EN60068-2-29:1993 (Or Equivalent), 40g 6ms Pulse
Duration
Shock Test: MIL-STD-202G (Or Equivalent), 100g 6ms Pulse Duration
Vibration Test: MIL-STD-202G (Or Equivalent), 20g 5-500-5Hz
Please contact sales for any particular requirements. Alternatively
Cynergy3 can arrange product testing to other MIL, DEFSTAN or IEC
standards with various third party test houses for specific applications.
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