SampleProtect Switching Unit

Provides experimenters with an end-to-end method of protecting sensitive samples from accidental electrostatic discharge (ESD).

Full overview >

Can be used with Proteox, Teslatron and experimental measurement probes
High quality measurement grade cables
Low noise

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Overview

Overview

The SampleProtect Switching Unit (SPSU) is a 24-channel unit in a 3U high enclosure designed for 19” rack mounting. The 24 signal lines are configured in 12 twisted pairs. At the rear of the unit there are 2 x 50-way sub-D connectors. One connector is used to connect all the signal lines to the measurement probe (or cryostat), the second is a feed-through link to connect any of the lines to additional instrumentation as an alternative to the individual BNC and Twinax connectors on the front panel. The 50-way connectors accept the SPSU Measurement Cable (quoted separately). With this connection configuration, the unit switches can be used to switch any of the signal lines between signal, open, measurement ground or protective ground.

Sample Protect Switching Unit

3U high and designed for 19” rack mounting
2 x 50 way rear mounted sub-D connectors
- Connection to the signal lines of the measurement probe or cryostat
- Feed-through link to connect any of the lines to additional instrumentation (an alternative to using the individual BNC and Twinax on front panel)
Unit switches can be used to switch any of the signal lines between signal, measurement ground or protective ground.
Each signal line has a BNC or Twinax port for connection directly to measurement electronics or diagnostics.
High-quality make-before-break switches
- Low resistance Au contacts
- Sealed against moisture ingress to avoid future contact corrosion
Internal signal routings designed to minimise cross-talk
Line resistance kept to a minimum

The measurement cable is a carefully specified cable constructed of 13 twisted pairs, 10 pairs of 26 (19/38) AWG tinned Cu and 3 pairs of 22 (19/34) AWG tinned Cu. Each pair is individually screened with a foil screen. Each screen has external insulation to isolate it from all the other screens. Each screen also has a drain wire.

In addition, the cable has an overall foil screen which has internal insulation plus an external screen braid. The overall screen also has a drain wire. This construction facilitates overall screening with the outer screen connected to protective ground but in addition any pair can be screened to a specific measurement ground for that channel. The cross-talk increases with frequency as expected and is shown in specifications.

Sample Protect Sample Unit - SPSU

Item	Value
Temperature Range	0 to 40° C
Voltage rating	50 VRMS
Recommended Frequency Range	DC – 100 kHz
Mutual Capacitance	38 pF @1 kHz
Line Inductance	< 0.30 µH
Conductor DC line Resistance	< 0.18 Ω @20° C
Shield DC line Resistance	< 0.12 Ω @20° C

Cross-talk signal induced in channel 2 resulting from an excitation drive current in channel 1 plotted as a function of frequency:

Measurement Grade Cable

Item	Value	Value
26AWG pairs	26AWG pairs	22AWG pairs
Number of twists	12 /ft (minimum)	12 /ft (minimum)
Temperature Range	-40 to 80°C	-40 to 80°C
Voltage rating	300VRMS	300VRMS
Mutual Capacitance	30pF/ft @ 1kHz	38pF/ft @ 1kHz
Ground Capacitance	54pF/ft @ 1kHz	68pF/ft @ 1kHz
Characteristic Impedance	55Ω	43Ω
Line Inductance	0.18µH/ft	0.16µH/ft
Conductor DC line Resistance	38Ω / 1000ft @ 20°C	15.5Ω / 1000ft @ 20°C
Shield DC line Resistance	34Ω / 1000ft @ 20°C	14.5Ω / 1000ft @ 20°C

Cross-talk signal induced in one conductor of a twisted pair resulting from an excitation drive current in a conductor of another twisted pair in the same cable construction, plotted as a function of frequency. Each pair is shielded with shields grounded to instrument ground:

The crosstalk measurements shown were measured on a 180cm length of cable. Cross-talk increases with frequency as expected.