14.2 Extended Channels (T7 Only) [T-Series Datasheet] | LabJack
 
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14.2 Extended Channels (T7 Only) [T-Series Datasheet]

Overview - T7 Only

The T7 has 14 built-in analog inputs (AIN0 through AIN13). For applications that need more, up to 112 total external analog inputs can be utilized by multiplexing the built-in analog inputs. Each built-in analog channel may be multiplexed into 8 new channels, where the starting extended channel number is:

startingExtendedChannel = builtinChannel * 8 + 16

The extended channel range begins at AIN16.

When a built-in channel is multiplexed, the original channel number becomes unavailable.

For example, if AIN4 is multiplexed, AIN48 through AIN55 are exposed as usable AIN and AIN4 is no longer available.

Differential Channels Pairings

For differential channels in the extended range, a channel may be the positive channel if it is one of the following ranges:

  • AIN16 through AIN23
  • AIN32 through AIN39
  • AIN48 through AIN55
  • AIN64 through AIN71
  • AIN80 through AIN87
  • AIN96 through AIN103
  • AIN112 through AIN119

The negative channel is 8 higher than the positive channel. For example, the positive channel AIN48 is paired with AIN56 as the negative channel.

The differential channel pairs for the built-in AIN0 through AIN13 are adjacent even/odd pairs such that the positive channel is even and the negative channel is greater than the positive channel by 1. Since the built-in AIN are multiplexed as described above, an extended negative channel is 8 higher than its corresponding extended positive channel. For example, a valid differential extended channel pair would be a positive channel of AIN70 and AIN78 as the negative channel, since:

  • AIN70 maps to AIN6 and
  • AIN78 maps to AIN7.

For more information on differential extended channels, see the Mux80 Datasheet.

MIO

The DB37 connector has 3 MIO lines designed to address expansion multiplexer ICs (integrated circuits), allowing for up to 112 total external analog inputs. Whenever a read is done on analog input channel numbers 16 to 127, the T7 will automatically control the MIO lines to read the correct multiplexed AIN. 

Mux80

The Mux80 accessory is used to multiplex AIN4 through AIN13, expanding them from 10 inputs to 80 inputs. AIN0 through AIN3 are still available (on the screw terminals of the T7). The extended channels can be read using the following registers. For further details, see the Mux80 Datasheet.

Mux80 Extended Channels
Name Start Address Type Access

AIN#(48:127)             Returns the voltage of the specified analog input.

96 FLOAT32 R

Note that when using the Mux80 board, the T7's MIO(0-2) lines are consumed for multiplexer signaling.

AIN Configurations on the Mux80

Use the following registers to configure AIN on the Mux80.

Name Start Address Type Access

AIN#(48:127)_NEGATIVE_CH             Specifies the negative channel to be used for each positive channel. 199=Default=> Single-Ended.

41048 UINT16 R/W

AIN_ALL_NEGATIVE_CH             A write to this global parameter affects all AIN. Writing 1 will set all AINs to differential. Writing 199 will set all AINs to single-ended. A read will return 1 if all AINs are set to differential and 199 if all AINs are set to single-ended. If AIN configurations are not consistent 0xFFFF will be returned.

43902 UINT16 R/W

More details about single-ended vs differential are in the Single-ended or Differential section of the main AIN page.

Resolution Index Registers
Name Start Address Type Access

AIN#(48:127)_RESOLUTION_INDEX             The resolution index for command-response and AIN-EF readings. A larger resolution index generally results in lower noise and longer sample times.

41548 UINT16 R/W

AIN_ALL_RESOLUTION_INDEX             The resolution index for command-response and AIN-EF readings. A larger resolution index generally results in lower noise and longer sample times. A write to this global parameter affects all AIN. A read will return the correct setting if all channels are set the same, but otherwise will return 0xFFFF.

43903 UINT16 R/W

STREAM_RESOLUTION_INDEX             The resolution index for stream readings. A larger resolution index generally results in lower noise and longer sample times.

4010 UINT32 R/W

More details about resolution are in the Resolution Index section of the main AIN page.

Range Registers
Name Start Address Type Access

AIN#(48:127)_RANGE             The range/span of each analog input. Write the highest expected input voltage.

40096 FLOAT32 R/W

AIN_ALL_RANGE             A write to this global parameter affects all AIN. A read will return the correct setting if all channels are set the same, but otherwise will return -9999.

43900 FLOAT32 R/W

More details about range are in the Range / Gain section of the main AIN page.

Settling Registers
Name Start Address Type Access

AIN#(48:127)_SETTLING_US             Settling time for command-response and AIN-EF readings.

42096 FLOAT32 R/W

AIN_ALL_SETTLING_US             Settling time for command-response and AIN-EF readings. A write to this global parameter affects all AIN. A read will return the correct setting if all channels are set the same, but otherwise will return -9999. Max is 50,000 us.

43904 FLOAT32 R/W

STREAM_SETTLING_US             Time in microseconds to allow signals to settle after switching the mux. Does not apply to the 1st channel in the scan list, as that settling is controlled by scan rate (the time from the last channel until the start of the next scan). Default=0. When set to less than 1, automatic settling will be used. The automatic settling behavior varies by device.

4008 FLOAT32 R/W

More details about settling are in the Settling section of the main AIN page.

Custom Multiplexing Applications

Custom multiplexing and signal conditioning boards can be designed and automatically controlled by a T7 using the DG408 multiplexing IC from Intersil.  The DG408 multiplexing IC from Intersil is the  recommended multiplexer, and a convenient ±12 volt power supply is available on the DB37 so the multiplexers can pass bipolar signals (see Vm+/Vm- documentation in Section 16.0).  These are the same ICs that do the device's internal channel multiplexing as well as the ICs integrated into the Mux80.  Figure 14.2.1 shows the typical connections for a pair of multiplexers.

T7 DG408 Multiplexers example circuit for analog input multiplexing.
Figure 14.2.1 Typical DG408DVZ Multiplexer Connections.

Below is a table indicating the MIO states required for controlling 14 DG408 multiplexing ICs that each route to a single AIN line and the extended analog input channel that must be read for a single-ended signal to be measured correctly.

Output State   Expanded Channel Multiplexing Mapping
MIO0 MIO1 MIO2   AIN0 AIN1 AIN2 AIN3 AIN4 AIN5 AIN6 AIN7 AIN8 AIN9 AIN10 AIN11 AIN12 AIN13
                                   
0 0 0   16 24 32 40 48 56 64 72 80 88 96 104 112 120
1 0 0   17 25 33 41 49 57 65 73 81 89 97 105 113 121
0 1 0   18 26 34 42 50 58 66 74 82 90 98 106 114 122
1 1 0   19 27 35 43 51 59 67 75 83 91 99 107 115 123
0 0 1   20 28 36 44 52 60 68 76 84 92 100 108 116 124
1 0 1   21 29 37 45 53 61 69 77 85 93 101 109 117 125
0 1 1   22 30 38 46 54 62 70 78 86 94 102 110 118 126
1 1 1   23 31 39 47 55 63 71 79 87 95 103 111 119 127

More information about adding your own multiplexers can be found in Section 2.6.1 of the U6 Datasheet.

Differential Tables

The tables below show which channels are positive (Pos) or negative (Neg) when paired differentially.  Additional information about using differential analog inputs with extended channels can be found in the Mux80 datasheet.

Built-in AIN (not multiplexed):

Pos Neg
0 1
2 3
4 5
6 7
8 9
10 11
12 13
   

AIN0 and AIN1 (multiplexed with an external multiplexer):

Pos Neg
16 24
17 25
18 26
19 27
20 28
21 29
22 30
23 31
   

AIN2 and AIN3 (multiplexed with an external multiplexer):

Pos Neg
32 40
33 41
34 42
35 43
36 44
37 45
38 46
39 47
   

AIN4 and AIN5 multiplexed with the Mux80 (or an external multiplexer):

Pos Neg
48 56
49 57
50 58
51 59
52 60
53 61
54 62
55 63
   

AIN6 and AIN7 multiplexed with the Mux80 (or an external multiplexer):

Pos Neg
64 72
65 73
66 74
67 75
68 76
69 77
70 78
71 79
   

AIN8 and AIN9 multiplexed with the Mux80 (or an external multiplexer):

Pos Neg
80 88
81 89
82 90
83 91
84 92
85 93
86 94
87 95
   

AIN10 and AIN11 multiplexed with the Mux80 (or an external multiplexer):

Pos Neg
96 104
97 105
98 106
99 107
100 108
101 109
102 110
103 111
   

AIN12 and AIN13 multiplexed with the Mux80 (or an external multiplexer):

Pos Neg
112 120
113 121
114 122
115 123
116 124
117 125
118 126
119 127