ISO 3171 Petroleum liquids - Automatic pipeline sampling
9 Control equipment
9.1 Function
The functions of the control equipment for an automatic sampler are to control the separating device to take either a flow-proportional sample or a fixed-rate sample, and it may also include a system to
a) continuously monitor the number of grabs and the volume of sample collected;
b) verify, at any time during sampling, the proportionality between the sample collection rate and the pipeline flow rate if operating in the flow-proportional mode.

NOTE - Continuous monitoring of density be used as an added monitoring facility.

9.2 Control equipment
9.2.1 The control equipment may be remote from the sampler in a control centre. Alternatively, it may be local to the sampler, in which case consideration should be given to the electrical safety classification of the hazardous area in which it is installed.

9.2.2 The control equipment should enable the operator to
a) set the equipment for the prospective cargo or batch size or for the necessary sampling ratio to meet the required operating criteria (see 14.2)
b) put the sampler into operation, and switch it off.

9.2.3 Facilities should be provided for monitoring the following during operation:
a) the flow rate in the main pipeline;
b) the sample receiver to indicate that the sample volume collected is proportional to the totalized flow in the main pipeline;
c) the number of grabs.

9.2.4 The equipment should provide an alarm if the flowmeter is indicating flow but no sampling is taking place and vice versa.

9.2.5 Alarms are recommended for
a) high level in the sample receiver;
b) low flow in the main Pipeline;
c) low flow in the sample loop;
d) loss of power;
e) sampling probe failure (for motor-driven probes).