RECOMMENDED ANALOG INPUT CONNECTION SCHEMES

This section describes analog input connection schemes to the DT3362 series AjD boards. Each connection scheme is discussed separately, with a diagram representing the connection. Input modes possible with each model of the DT3362 series are indicated in Table 4-7.

SYSTEM INTERCONNECTIONS

TABLE 4-7: DT3362 SERIES INPUT MODES INPUT MODE

PSEUDO-MODEL SE 01 01

DT3362-SDI/16SE Yes Yes Yes

DT3362-320I/64SE Yes Yes Yes

DT3362-SDI/16SE-PGH Yes Yes Yes DT3362-32DI/64SE-PGH Yes Yes Yes

DT3362-F-SOI No No Yes

DT3362-F-3201 No No Yes

DT3362-F-16SE Yes Yes No

OT3362-F-64SE Yes Yes No

OT3362-G-SDI No No Yes

DT3362-G-32DI No No Yes

DT3362-G-16SE Yes Yes No

DT3362-G-64SE Yes Yes No

DT3362-H-SDI No No Yes

DT3362-H-32DI No No Yes

DT3362-H-16SE Yes Yes No

DT3362-H-64SE Yes Yes No

DT3362-H-SDI-PGH No No Yes

DT3362-H-32DI-PGH No No Yes

DT3362-H-16SE-PGH Yes Yes No

DT3362-H-64SE-PGH Yes Yes No

DT3377 No No Yes

DT336S-4SE Yes No No

DT336S-12SE Yes No No

4.6.1 SINGLE-ENDED INPUTS

SYSTEM INTERCONNECTIONS RECOMMENDED ANALOG INPUT CONNECTION SCHEMES

In single-ended connections, input signals have a common low side which is connected to the Analog Ground (AGND, pin 17 of J3, or pins 49 and 50 of J2). This connection scheme gives you maximum channel density. The ma~~r d~~advantage of the single-ended connection scheme ~5 ~nat ~ne instrumentation amplifier does not provide common mode rejection of the input signal, as it does in differential input connections. The' single-ended connection scheme is available on models DT3362-16SE/8DI, DT3362-64SE/32DI, DT3362-16SE/8DI-PGH, DT3362-64SE/32DI-PGH, DT3362-F-16SE, DT3362-F-64SE, DT3362-G-16SE, DT3362-G-64SE, DT3362-H-16SE, DT3362-H-64SE, DT3362-H-16SE-PGH, DT3362-H-64SE-PGH, DT3368-4SE, and DT3368-12SE. Figure 4-5 shows how to connect single-ended inputs to these boards.

NOTE

When operating in this input scheme, the user should always reference Amp Lo (AMP IN) to Analog Ground. This is accomplished by connecting Amp Lo to Analog Ground (pin 18 to pin 17 of the J3 connector). Failure to do so will result in inaccurate data conversions. In expanded versions, Amp Lo is tied only on the J3 connector. The DT3368-4SE and DT3368-12SE have no Amp Lo connection. In both cases the return point of each channel should be tied directly to Analog Ground.

Single-ended inputs should be restricted to short lead lengths (less than 15 feet) and gains less than 10.

SYSTEM INTERCONNECTIONS

RECOMMENDED ANALOG INPUT CONNECTION SCHEMES

Pin 1

V1~_

I

^{16 ','}

AGNO .

---~~----~---1~8~Or---~~

TPC00027

ALL MODELS EXCEPT DT3368-4SE AND DT3368-12SE

11~-~

i

TPC00013

MODELS DT3368-4SE AND DT3368-12SE NOTES:

1. All signal inputs must be referenced to Analog Ground.

2. All unused analog input channels should be connected to Analog Ground. Failure to do so can result in inaccurate AID conversions on all other channels, those closest to the

floating channel(s) being affected most.

FIGURE 4-5: SINGLE-ENDED INPUT CONNECTION

SYSTEM INTERCONNECTION~

RECOMMENDED ANALOG INPUT CONNECTION SCHEME~

4.6.2 PSEUDO-DIFFERENTIAL INPUTS

The pseudo-differential input is a variation of the single-ended input which provides the user with some degree of common mode noise rejection without sacrificing the number of input channels. To implement this input mode, the user jumpers the board for single-ended inputs and ties all the return sides of the single=ended inputs to the low side of the instrumentation amplifier (Amp Lo). This is possible if the Amp Lo connection is brought out to the user input connector, such as a screw terminal panel. Amp Lo in turn is connected externally to Analog Ground via

i

to 10 kilohm resistor. In this manner the input instrumentation amplifier can reject the common mode noise. Figure 4-6 shows how to connect the Amp Lo

(AMP IN) and AGND pin for pseudo-differential operation.

NOTE

The pseudo-differential input scheme can be applied only to channels served by the J3 connector on DT3362-16SE/8DI, DT3362-64SE/32DI, DT3362-16SE/8DI-PGH, DT3362-64SE/32DI-PGH, DT3362-F-16SE, DT3362-F-64SE, DT3362-G-16SE, DT3362-G-64SE, DT3362-H-16SE, DT3362-H-64SE, DT3362-H-16SE-PGH and DT3362-H-64SE-PGH~ It is typically used with lead lengths not exceeding 25 feet and gains no more than 10. Channels served by the J2 connector cannot accommodate pseudo-differential connections since the expansion module does not provide an Amp Lo pin for connection of the return lines. For the same reason, the DT3368-4SE and DT3368-12SE do not accommodate pseudo-differential connection schemes.

SYSTEM INTERCONNECTIONS

RECOMMENDED ANALOG INPUT CONNECTION SCHEMES

1~

I ,

! _I_,

. .

^I_I

I I :

, I I

AMP LOW

AGND

~

^TPC00038

NOTES:

1. All signal inputs must be referenced to Analog Ground.

2. All unused analog input channels should be connected to Analog Ground. Failure to do so can result in inaccurate AID conversions on all other channels, those closest to the

floating channel(s) being affected most.

3. Rcm is user-supplied bias return resistor. Its value is typically between 1 and 10 kilohms.

FIGURE 4-6: PSEUDO-DIFFERENTIAL INPUT CONNECTION

4.6.3 DIFFERENTIAL INPUTS

SYSTEM INTERCONNECTIONS RECOMMENDED ANALOG INPUT CONNECTION SCHEMES

In a differential input scheme, two multiplexer switches are used on each channel. Thus the number of channels which can be accommodated is cut in half. The benefits are that the common mode voltages, that is, voltages common to both the high and low side of an analog input, ~all be rejected ^by the differential input instrumentation amplifier. This common mode

rejection results in a much quieter system. This input confiQuration can be used with inDut ranaes as low as lOmV full scale-with twisted pair (low level) shielded--input cables.

Lead lengths may suit user requirements but should be kept as short as possible.

NOTE

The low end of each differential input must be referenced to Analog Ground. This can be done by connecting a 1 to 10 kilohm resistor between the low end of each differential input and Analog Ground. If all inputs share a common ground, a single 10 kilohm resistor can be connected between the input signal common and the board Analog Ground.

The DT3362 series boards which can be operated differentially are the following: DT3362-16SE/8DI, DT3362-64SE/32DI, DT3362-165E/8DI-PGH, DT3362-64SE/32DI-PGH, DT3362-F-8DI, DT3362-F-32DI, DT3362-G-8DI, DT3362-G-32DI, and DT3377. Figure 4-7 shows how to connect a differential input.

SYSTEM INTERCONNECTIONS

RECOMMENDED ANALOG INPUT CONNECTION SCHEMES

RemO VemO

17 _TPC00039

NOTES:

1. All signal inputs must be referenced to Analog Ground.

2. All unused analog input channels should be connected to Analog Ground. Failure to do so can result in inaccurate AID conversions on all other channels, those closest to the

floating channel(s) being affected most.

3. Rcm is user-supplied bias return resistor. Its value is typically between 1 and 10 kilohm.

FIGURE 4-7: DIFFERENTIAL INPUT CONNECTION

Dans le document SERIES DT3362 (Page 82-90)