Appx.
12
Measuring Multiple Targets
Appx. 6
Measuring Multiple Targets
To measure multiple targets with a single instrument, you will need to provide an external switching
relay. Please note the following important considerations when designing the switching device:
Relay selection
(1)
Choose a relay with low thermal electromotive force.
Thermal electromotive force increases in the following order:
Latching < OptoMOS relays < Single-stable (high sensitivity) relays < Single-stable relays
(2)
Choose a relay that delivers stable contact performance even under minuscule load.
Power relays experience poor contact under conditions of minuscule load. Be sure to use a relay
designed for use with low signals or an OptoMOS relay.
(3)
Choose a relay whose contacts have a rated voltage that is at least 200% greater than the
switching voltage.
A relay with a rated voltage of 110 V will support a switching voltage of 55 V or less.
(4) When using an OptoMOS relay, choose a relay with a small output pin capacitance.
When the capacitance, calculated by multiplying the output pin capacitance by the number of
contacts, increases, the contact check function will generate a result of “connected” even when all
contacts are open.
(5) When the instrument’s input resistance is set to 10 M
Ω
, measured values may decrease due to
the effects of contact resistance.
Example: An error of 1 ppm will occur if the contact resistance is 10
Ω
and the input resistance is
10 M
Ω
.
(6) Examples of appropriate relays
Panasonic ATXS20620: High sensitivity, 4.5 V single-stable, suitable for use with minuscule loads
Panasonic AT26620:
4.5 V latching, suitable for use with minuscule loads
Panasonic AQW216:
OptoMOS relay, max. 120
Ω
on-resistance, 50 pF output pin capacitance
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