A-M Systems 2200 Manuel d'instruction - Page 13

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The operation of the Model 2200 is summarized in the block diagram (see Fig. 4). The input

signal is buffered, then enabled or disabled by an analog gate. When disabled, the output

voltage at this stage is zero. A linear optoisolator system is used to couple the signal to the

isolated section. The isolated signal is amplified (and possibly converted to a current)

according to the Range setting.

The output amplifier is connected as a voltage-gain amplifier in voltage modes, with different

feedback resistances depending on the setting. In the current mode, the same amplifier is

used to fix a virtual ground within the instrument. The two currents connected to this virtual

ground are the set current, determined by the range switch and input signal amplitude; and

the load, driven by the amplifier output

With the Control Gate input signal open (disconnected), or set to a logical I by an external

signal, the signal propagates normally as described above. If the Gate is set to a logical 0, the

internal signal is connected to the input ground instead of the input signal.

Output errors are measured by sensing the output amplifier's differential input voltage. If for

any reason the amplifier fails to deliver the requested signal, a warning LED illuminates and

the Error output pin is set to a TTL-high level.

Two sets of batteries are used to power the 2200. Note that the BATTTERY tester only detects

the present state of the batteries, and does not indicate how long the charged batteries will be

able to support the load. The batteries used in the 2200 vary more from unit to unit than from

fullly-charged to nearly-discharged, making it impractical to measure the charge state. It is

recommended that you, the user, keep track of battery usage to ensure that the battery does

not become exhausted at a critical time.

A-M Systems

Theory of Operation

Figure 4. Instrument block diagram

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