TS-8820-ADC

From Technologic Systems Manuals

The TS-8820 offers 16 channels of single ended bi-polar ADC inputs. These ADC inputs are provided by two separate 8 channel ADC devices. Each ADC controller supports a selectable voltage (via GPIO from the SoM, see below) ranges of -5 V to +5 V as well as -10 V to +10 V. This means that each set of 8 channels can be set to different ranges. Each set of 8 channels are sampled simultaneously inside the ADC device.

All 16 ADC inputs are located on the P3, P4, and P5 terminal blocks. While each ADC has a pair of inputs, they are single ended ADC channels; all negative input terminals connect to the TS-8820 common ground.

Additionally, the ADC devices support a number of oversampling options, also controlled via GPIO from the SoM. Enabling oversampling has the effect of adding a digital filter function after the ADC. Increasing the oversampling ratio will decrease the effective sampling rate of the ADC but will increase the signal to noise ratio of each channel. The oversampling rate is shared between both ADC devices, that is, the rate can not be independently set per-device.

Setting the ADC voltage range:

ADC chan. 1 - 8
DIO Val Range
CN2_56 1 -10 V to +10 V
CN2_56 0 -5 V to +5 V
ADC chan. 9 - 16
DIO Val Range
CN2_58 1 -10 V to +10 V
CN2_58 0 -5 V to +5 V

Setting the oversampling rate:

CN2_64 CN2_62 CN2_60 OS Rate
0 0 0 N/A
0 0 1 2
0 1 0 4
0 1 1 8
1 0 0 16
1 0 1 32
1 1 0 64
1 1 1 Invalid
Note: SoM GPIO pins will usually start as inputs with pull up resistors. Therefore the default range will likely be -10 V to +10 V with an invalid oversampling rate. It is advised to set up these pins before acquiring ADC samples.

1 Current Loops (4-20 mA measurement)

All 16 ADC channels independently support 4-20 mA current loop measurements. This is achieved by setting a pin jumper for the respective channel on the current loop enable pin header. Setting a jumper will electrically enable a 200 Ω 0.5% resistor from the ADC channel to ground allowing for a constant current measurement.

2 Thermistor

The TS-8820 supports up to 8 thermistors on channels 1 though 8. Support for a thermistor is enabled via software, the ADC pullup bit of TS-8820 FPGA register 0x2. Setting bit 8 enables a pull up on ADC channels 1 and 2, setting bit 9 enables a pull up on ADC channels 3 and 4, and setting bit 10 enables a pull up on channels 5 through 8. When enabled, each channel will get a separate 6.04 kΩ resistor to +12.5 V allowing the use of a thermistor probe.

3 ADC Usage

The 'ts8820ctl' application can be used to quickly sample the ADCs. This will send simultaneous sampling commands to each of the two ADC devices which will then sample all 16 channels in total the amount of times specified. See the "ts8820ctl.c" and "ts8820.c" files for examples on how this operation takes place.

For example, to sample all of the channels 5 times, the following command would be used:

ts8820ctl --sample=5

Collected 80 samples total.
  
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Ch 9 Ch10 Ch11 Ch12 Ch13 Ch14 Ch15 Ch16 
---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- 
-7626 2195 2193 2199 2192 2195 2195 2192 2189 2189 2193 2190 2189 2192 2191 2191 
-7626 2194 2192 2198 2191 2194 2194 2191 2188 2189 2192 2189 2188 2191 2189 2190 
-7626 2193 2191 2197 2190 2193 2193 2190 2187 2188 2191 2188 2186 2190 2189 2189 
-7626 2189 2188 2193 2186 2189 2190 2186 2183 2184 2187 2184 2183 2186 2185 2185 
-7626 2189 2187 2192 2186 2188 2189 2186 2183 2183 2187 2184 2182 2185 2184 2185

Above, channel 1 has a -7.62 V voltage source attached to it, all other channels are left unconnected. The range is set at -10 V to +10 V, and the oversampling rate is set to 64.