Formers
Our standard range of resistors are wound on round and oval
section formers of high grade insulating ceramic. Stock sizes and designations are
given in
Table 1. Other former lengths and shapes or materials can be used to meet customer specifications,
e.g. we are volume producers of special resistance windings on fibreglass and "flexible"
Bakelite cores to supply the original equipment requirements of Australian Car and
Electrical Appliance Manufacturers.
Resistance Wire
Resistance stability is maintained throughout the
operating temperature range by the exclusive use of resistance wires having a temperature
co-efficient of 20 ppm. Wires with particular temperature co-efficient characteristics
can be used to supply customer special order requirements. Resistance winding wires
are silver soldered to the terminating bands to ensure reliability even under overload
conditions.
Resistor Coating
This Tropic-Proof coating compounded with a special silicone
resin has been developed to withstand high operating temperatures and thermal cycling
while retaining excellent electrical insulation and moisture resistance. Resistors
with this coating are rated at full load to a temperature rise of 250°C above an ambient of 20°C, but independent tests
prove that surface temperatures up to 350°C can be maintained continuously.
Quality Control
Our winding technique accurately monitored at near zero tension
together with controlled temperature cycling during coating ensures maximum stability.
Each stage of manufacture is subject to close quality control checks which together
with individual final inspection and testing maintains our high standards of reliability.
Standard Terminations
Axial leads on Types HTR 3, HTR 5 and HTR 10. Solder lugs
on 20 Watt and larger, on both round and oval formers. Lug width is 4.8mm on all
oval formers and HTR 20 - HTR 30, 6.3mm on HTR 40 - HTR 75, all others are 9.6mm.
Fixed and adjustable tapping bands on all formers HTR 20 and larger.
Other types of terminations to special order e.g. solder lugs on HTR 5 and 10 sizes,
provision for bolt and nut or "push-on" connectors and brass ferrule ends.
Resistance Range
Through using only the highest quality resistance wires, we
can offer the widest "Standard Range" of resistance values to former size available.
Values above and below those listed in
Table 1. but tolerances down to 0.1% are
readily available for all types.
Tolerance
Standard tolerance 5% 10 ohms and above, 10% below 10
ohms, these tolerances apply throughout the range as listed in
Table 1 but tolerances down to 0.1% are readily available for all types.
Tolerances of less than 0.1% Matched Pair, Resistor Chains etc, can be supplied to special order.
Stability
Better than 0.02% per 1000 hours running at maximum load at 70°C.
Mounting Feet
Horizontal mounting feet are available for all oval formers
and round formers of 14.5mm nominal diameter and larger. These right-angle brackets
are desigend to locate into the ends of the former and mount the resistor body parallel
to the supporting panel. Their use does not add to the width of the resistor but
raises the overall height of the unit above the support panel as follows:
- Types HTR 20 through to HTR 75: 30mm
- Types HTR 65 through to HTR 200: 50mm
- Types HTR 350: 80mm
- Types HTR 500 through to 1000: 92mm
- All oval types: 160mm
Holes in the bracket, slotted along the axis of the resistor,
provide for fixing to the support panel - the screw diameters being 4mm for types
HTR 20, 25, 30, 40, 50 & 75, and 5mm for all other types.
The distance required between holes for assembly are listed in
Table 1.
Heat-sink mountings have been developed for all 14.5mm outer diameter formers which increases
their power-handling capacity by up to 50% when attached to 40cm² of metal
chassis area, by the 4mm diameter screw provided.
